[Keyboard] Bathroom Epiphanies Frosty Flake rev 20130602 (#15365)

* add optional support for Frosty Flake rev 20130602

* update documentation with instructions on building for rev 20130602

* support revisions using subfolders instead of preprocessor directives

* rules.mk cleanup

keyboards/bpiphany/frosty_flake/20130602/rules.mk

@@ -0,0 +1,22 @@
+# MCU name
+MCU = atmega32u2
+
+# Bootloader selection
+BOOTLOADER = atmel-dfu
+
+# Build Options
+#   change yes to no to disable
+#
+BOOTMAGIC_ENABLE = no       # Enable Bootmagic Lite
+MOUSEKEY_ENABLE = yes       # 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 = no            # Enable N-Key Rollover
+BACKLIGHT_ENABLE = no       # Enable keyboard backlight functionality
+AUDIO_ENABLE = no           # Audio output
+
+CUSTOM_MATRIX = lite
+SRC += 20130602/matrix.c
+
+LAYOUTS = tkl_ansi