[Keymap] Add issmirnov {user, ergodox, levinson} files. (#7239)

* Add issmirnov {user, ergodox, levinson} files.

There are enough interesting QMK tricks in these layouts that it seems
worth it to share with the broader community. Big thanks to Drashna for
inspiration, as well as all the wonderful creators of QMK documentation.

Some highlights:
- Common layout shared between levinson and ergodox_ez
- TAP_TOG macro for fast layer switching
- Autogenerated keymaps ascii art with git hooks

I will do my best to do periodic rolls here, but the source of truth
will always be https://github.com/issmirnov/qmk-keebs

* Incorporate review feedback.

- Remove CLEAR_EEPROM in favor of built in EEP_RST
- Remove custom handlers for audio on bootup and shutdown
- Remove plethora of unneeded includes
- Remove deprecated and dupliated config options

HUGE thanks to drashna for the review!

* Apply suggestions from code review

Huge thanks to drashna@ for a very thorough review and the very useful suggestions.

Co-Authored-By: Drashna Jaelre <drashna@live.com>

* Remove unclear optimization

This was an artifact from some other keymap I saw.

1 files changed, 43 insertions, 0 deletions

diff --git a/users/issmirnov/issmirnov.c b/users/issmirnov/issmirnov.c
new file mode 100644
index 0000000000..665afbcfd7
--- /dev/null
+++ b/users/issmirnov/issmirnov.c
@@ -0,0 +1,43 @@
+#include "issmirnov.h"
+
+enum combo_events {
+  JK_ESC,
+  DF_CLN,
+  SD_SLASH,
+  XC_COPY,
+  XV_PASTE
+};
+
+
+const uint16_t PROGMEM jk_combo[] = {KC_J, KC_K, COMBO_END};
+const uint16_t PROGMEM df_combo[] = {KC_D, KC_F, COMBO_END};
+const uint16_t PROGMEM sd_combo[] = {KC_S, KC_D, COMBO_END};
+const uint16_t PROGMEM copy_combo[] = {KC_X, KC_C, COMBO_END};
+const uint16_t PROGMEM paste_combo[] = {KC_X, KC_V, COMBO_END};
+
+
+// BE SURE TO UPDATE THE CONFIG.H "COMBO_COUNT" value when you add elements here!
+combo_t key_combos[COMBO_COUNT] = {
+  COMBO(jk_combo, KC_ESC),
+  COMBO(df_combo, KC_COLON),
+  COMBO(sd_combo, KC_SLASH),
+  [XC_COPY] = COMBO_ACTION(copy_combo),
+  [XV_PASTE] = COMBO_ACTION(paste_combo),
+};
+
+
+void process_combo_event(uint8_t combo_index, bool pressed) {
+  switch(combo_index) {
+    case XC_COPY:
+      if (pressed) {
+        tap_code16(LCTL(KC_C));
+      }
+      break;
+
+    case XV_PASTE:
+      if (pressed) {
+        tap_code16(LCTL(KC_V));
+      }
+      break;
+  }
+}