Creates a layouts/ folder for keymaps shared between keyboards (#1609)

* include variables and .h files as pp directives

* start layout compilation

* split ergodoxes up

* don't compile all layouts for everything

* might seg fault

* reset layouts variable

* actually reset layouts

* include rules.mk instead

* remove includes from rules.mk

* update variable setting

* load visualizer from path

* adds some more examples

* adds more layouts

* more boards added

* more boards added

* adds documentation for layouts

* use lowercase names for LAYOUT_

* add layout.json files for each layout

* add community folder, default keymaps for layouts

* touch-up default layouts

* touch-up layouts, some keyboard rules.mk

* update documentation for layouts

* fix up serial/i2c switches

layouts/community/ergodox/twey/readme.md

@@ -0,0 +1,17 @@
+# Twey's Home Configuration
+## Layers
+- Layer 0: Non-ANSI Dvorak layout, with modified modifiers — all
+  modifiers on thumb keys, as well as return and space.
+- Layer 1: Default symbol layout.
+- Layer 2: Plover-oriented stenography layer.
+- Layer 3: Extended media/mouse layout.
+
+## Unusual features
+The Plover key (top right key on the left half) also sends my Plover
+‘toggle’ chord (SH-FT) when pressed, as well as toggling the steno
+layer, so you can toggle between steno and typing modes with a single
+keypress.
+
+If you want to use this feature, you'll need to add the
+`commands.json` dictionary to your Plover dictionaries, or define the
+toggle stroke (`PHROLG`) yourself.