Keymap: Add am keymap (#3843)

* Add am keymap

* Add configuration to play nice with stuck modifiers

This is in particular useful with emacs since its easy to get ctrl stuck

* Deactivate mouse keys and backlight

* Add control/esc and shift/enter taps

* Remove DVORAK and PLOVER

I won't be using this soon, so getting some free space

* Raiser and Lower ideas from jeebak

* Add cursor and mouse layers

* Enable mouse keys

* Switch underscore with minus

* Disable audio and fix warnings

* Update to the upstream changes

* VIM line motion symbols on the raise layer

* Enable sound and freeup some media keys on layers

* Fix whitespace on keymap

* Code review changes

* Improve keymap documentation

* Improve keymap to match to the default one

* Restore DEFAULT_FOLDER to the default value

* Fix config.h unescaped line

keyboards/planck/keymaps/am/readme.md

@@ -0,0 +1,17 @@
+# The Am Planck Layout
+
+Heavily inspired by other layouts out there, and fine tuned to work well on emacs (most recently spacemacs with vim bindings).
+
+It features:
+
+- Media keys (bottom right)
+- Focused on Qwerty and Colemak
+- Number pads (normal and reversed)
+- TouchCursor layer
+- Mouse layer
+
+## Build
+
+Making planck/rev4 with keymap am and target dfu
+
+    make planck/rev4:am:dfu