[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/config.h

@@ -0,0 +1,14 @@
+// Copyright 2021 Gabriel Kim (@gabrielkim13)
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#define MATRIX_ROW_PINS \
+    { B15, A8, A9, B14, A15, B3 }
+#define MATRIX_COL_PINS \
+    { B4, B5, B6, B7, B8, B9, A1, A2, A3, A4, A5, A6, A7, B0, B1, A0, B10 }
+#define UNUSED_PINS \
+    { A10, A11, A12, B2, B12, C14, C15 }
+
+#define LED_CAPS_LOCK_PIN C13
+#define LED_PIN_ON_STATE 0