[Keymap] bcat keymaps and userspace (#10705)

Add Eco keymap, factor Crkbd keymap to community layout, other minor tweaks

* Remove outdated Crkbd Ctrl key positioning info

* Add Left Alt key to Lily58 keymap

* Lily58 no longer overrides default TAPPING_TERM

* Refactor Crkbd keymap to use new community layout

* Fix underglow animations for Crkbd w/ Split Common

* Add initial Eco keymap

* Update outdated reference to Crkbd layout

* Add keymap links to userspace readme

* Add copyright notices to files changed in this PR

1 files changed, 126 insertions, 0 deletions

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+# bcat's split 3x6 + 3 thumb keys layout
+
+This is my favorite split ergo layout for typing, featuring the traditional
+four ortho/ergo layers (Default, Lower, Raise, Adjust). It is loosely inspired
+by the default Planck (numbers on Lower, symbols on Raise) and Crkbd (Space on
+left, Enter on right) layouts, but has since been redesigned heavily according
+to the principles described below.
+
+* Since my most-frequently-used keyboard shortcuts involve Ctrl, which lives on
+the left half of the keyboard, keys frequently used with it (numbers, function
+keys, etc.) are on the Raise layer activated by the right thumb.
+
+* Navigation can be done on the right half alone, to enable simultaneous
+left-handed mousing. Additionally, Web pages can be scrolled with Space or
+Shift+Space on the left half alone, to enable taking notes with the right hand
+at the same time.
+
+* Other than Right Shift (which I seldom use), mods aren't rebound on layers.
+
+* Likewise, Backspace is not rebound on layers to avoid having to let go of
+layer-switch keys to correct mistakes.
+
+## Default layer
+
+![Default layer layout](https://i.imgur.com/g5N7g8D.png)
+
+([KLE](http://www.keyboard-layout-editor.com/#/gists/08d9827d916662a9414f48805aa895a5))
+
+* The alpha keys are a standard QWERTY layout, no funny business there.
+
+* Tab and Backspace are in familiar locations from my row-staggered boards
+(almost all of which use HHKB-style split backspace).
+
+* The Esc key is next to the home row for convenience in Vim.
+
+* There are two Shift keys, although I generally use Left Shift. (I've
+considered replacing Right Shift with another key, but haven't chosen one.)
+
+* Lower and Raise layer-switch keys are in the resting position of my left and
+right thumbs, respectively.
+
+* Space and Enter are on the big thumb keys so they're easy to press.
+
+* Ctrl is on the left for ease of chording, especially one-handed use of common
+shortcuts like Ctrl+T and Ctrl+W. This puts Alt on the right by the process of
+elimination. (I would really like one more 1U thumb key on each half to allow
+for a redundant Alt key on the left and a dedicated Super key on the right.)
+
+## Lower layer
+
+![Lower layer layout](https://i.imgur.com/vaIc9JY.png)
+
+([KLE](http://www.keyboard-layout-editor.com/#/gists/c3fba5eaa2cd70fdfbdbc0f9e34d3bc0))
+
+* This could also be called the "symbol layer".
+
+* Shifted numbers are bound in their usual positions on the top row.
+
+* Hyphen/Underscore and Equals/Plus are in the right index- and middle-finger
+columns for easy reach. They share the same relative position as on a
+row-staggered keyboard, and the shifted versions are physically above the
+unshifted versions as a mnemonic device.
+
+* Brackets and braces are placed below the parens for easy recall. Once again,
+the shifted versions are on the home row and the unshifted versions are on the
+bottom row.
+
+* Forward Slash/Pipe and Backtick/Tilde fill out the remaining positions on the
+right half, with the same relative positions as on a row-staggered HHKB layout.
+And yup, the shifted versions are above the unshifted versions.
+
+* Remaining keys from a TKL are placed out of the way on the bottom row of the
+left half.
+
+* The home row on the left half contains handy shortcuts for zooming and browser
+navigation.
+
+* Lower+Esc is bound to Ctrl+Space because the Ctrl and Space keys are both on
+the left thumb, so this key combination (which I use for tmux prefix and editor
+autocomplete) is hard to press in its natural location.
+
+* Lower+Tab is bound to a custom Alt+Tab macro that keeps the Alt modifier held
+as long as the Lower key is held down. This means that window switching is on
+Lower+Tab immediately next to browser tab switching (Ctrl+Tab).
+
+## Raise layer
+
+![Raise layer layout](https://i.imgur.com/VNEiV9A.png)
+
+([KLE](http://www.keyboard-layout-editor.com/#/gists/08b44355d4ca85d294bad9e2821f91d7))
+
+* This could also be called the "number layer".
+
+* Unshifted numbers are bound in their usual positions on the top row.
+
+* Arrow keys are on VIM-style HJKL keys.
+
+* Home/End and Page Up/Page Down are in the same column as the arrow keys, but
+translated down one row. (This means that the comma and period keys are not
+bound on the number layer, which makes data entry a bit funky. I might add a
+dedicated numpad layer to compensate.)
+
+* Function keys F1–F10 take up most of remaining space on the left half, with
+F11 and F12 spilling over to the right half. (This puts the most used function
+keys (F1–F5) on the home row.)
+
+* Insert and Delete are on the rightmost column, because there didn't seem to
+be a better place to put them.
+
+* Caps Lock is bound in the same position as on an HHKB, for lack of an obvious
+better location.
+
+## Adjust layer
+
+![Adjust layer layout](https://i.imgur.com/fZouko5.png)
+
+([KLE](http://www.keyboard-layout-editor.com/#/gists/77e7572e077b36a23eb2086017e16fee))
+
+* Media keys are centered around the ESDF cluster, just like I arrange them on
+row-staggered keyboards. (It's even more sensible with columnar stagger.)
+
+* The navigation keys are replaced by RGB controls. Again, this mirrors the
+positioning I use on my row-staggered keyboards.
+
+* Finally, reset keys live at the top-left corner of the right half where it's
+reasonably hard to press them by accident.