[Keyboard] Add Meck TKL handwired (#15533)

* Add meck_tkl

* Fix configuration and pin assignment

* Rellocate A10 pin, as it is used by the USB DFU bootloader

* Add volume and media keys to the function keys layer

* Rellocate source files to the handwired keyboards folder and add documentation

* Review changes for PR
- Improve LAYOUT macro to match the keyboard layout.
- Use "kxy" as pin names on the LAYOUT macro.
- Remove unused mcuconf.h and halconf.h.
- Fix README.

* Improve layout macro naming

keyboards/handwired/meck_tkl/blackpill_f401/rules.mk

@@ -0,0 +1,10 @@
+# MCU name
+MCU = STM32F401
+
+# Bootloader selection
+BOOTLOADER = stm32-dfu
+
+# Build Options
+#   change yes to no to disable
+#
+KEYBOARD_SHARED_EP = yes