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/dvorak_plover/README.md

@@ -0,0 +1,14 @@
+Dvorak support, plover support, gaming support
+
+I'm used to the Kinesis, so originally I was just going to patch up
+the thumb keys to be more familiar. But the ergodox is really well
+suited to NKRO support in Plover, so I added a layer for that, and
+then I remembered that dvorak can be really annoying for video
+games (try to reach WASD), so I added a layer for that.
+
+The result is probably a bit idiosyncratic, but it works for me.
+
+(I also don't have any press/hold distinction keys, because that
+confuses my fuzzy little brain.)
+
+Contributed by seebs (seebs@seebs.net)