LFKeyboards Mini1800: refactor into revisions (#16260)

* fork Mini1800 into reva and revc versions

* update info.json

- apply friendly formatting
- update maintainer value

* update keymap rules.mk formatting

- align inline comments
- convert tabs to spaces

* align keymap rules.mk files to QMK template

* move common keymap rules.mk settings to revision level

* info.json: correct key sequence

* align revision rules.mk files to QMK template

* clean up revision rules.mk files

* add readme files for each revision

* correct USB Product string

* remove post_rules.mk files

The internal settings were commented out, so the files actually don't do anything.

* edit Bootloader instructions on main readme

* move non-assignment rules to post_rules.mk

* add inline comments for NKRO_ENABLE per fauxpark

keyboards/lfkeyboards/mini1800/reva/rules.mk

@@ -0,0 +1,29 @@
+# MCU name
+MCU = at90usb1286
+
+# Bootloader selection
+BOOTLOADER = atmel-dfu
+
+# Build Options
+#   change yes to no to disable
+#
+BOOTMAGIC_ENABLE = no       # Enable Bootmagic Lite
+MOUSEKEY_ENABLE = no        # Mouse keys
+EXTRAKEY_ENABLE = yes       # Audio control and System control
+CONSOLE_ENABLE = no         # Console for debug
+COMMAND_ENABLE = no         # Commands for debug and configuration
+NKRO_ENABLE = yes           # Enable N-Key Rollover
+BACKLIGHT_ENABLE = yes      # Enable keyboard backlight functionality
+RGBLIGHT_ENABLE = yes       # Enable keyboard RGB underglow
+AUDIO_ENABLE = yes          # Audio output
+
+# RGB code is implemented in lfkeyboards, not WS2812
+RGBLIGHT_CUSTOM_DRIVER = yes
+BACKLIGHT_DRIVER = custom
+SLEEP_LED_ENABLE = yes
+
+ISSI_ENABLE = yes           # If the I2C pullup resistors aren't install this must be disabled
+WATCHDOG_ENABLE = yes       # Resets keyboard if matrix_scan isn't run every 250ms
+
+# Extra source files for IS3731 lighting
+SRC = TWIlib.c issi.c lighting.c