[Keymap] Jonavin keymap kastenwagen48 (#15825)

Co-authored-by: Drashna Jaelre <drashna@live.com>
Co-authored-by: Jonavin <=>

keyboards/nopunin10did/kastenwagen48/keymaps/jonavin/readme.md

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+Jonavin Kastenwagen 48 Keymap
+Designed to match my other keymaps
+
+NOTE: Uses userpace user/jonavin
+
+Feature changes from Default
+  - Bottom row mapping LCtrl, LAlt, LGui, spacebars, MO(2)/LOWER, MO(1)/FN, RCtrl
+  - CAPS as MO(3)/RAISE - tap to toggle
+  - numpad in MO(3) layer
+  - double tap L Shift for CAPS
+  - RESET moved to under encoder in MO(2)
+  - implement Win Key Lock 
+  - GRV Escape overides
+  - ENCODERS
+    - TOP LEFT
+      - Volume up/down
+    - TOP RIGHT
+      - Left Shift held - change layers
+      - Right Shift held - Page Up/Down
+      - Left Ctrl held - navigate next/prev words
+      - Left Alt held - change media next/prev track
+      - RAISE + Encode push toggles between volume change and tab scrolling
+    - ENCODER_DIRECTION_FLIP has been defined to avoid issues with encoder going in opposition direction
+
+OPTIONS in rules.mk
+---------------------------------------
+
+STARTUP_NUMLOCK_ON = yes
+- turns on NUMLOCK by default
+
+ENCODER_DEFAULTACTIONS_ENABLE = yes
+- Enabled default encoder funtions
+- When enabled, use this in the keymap for an additional encoder processing 
+-   bool encoder_update_keymap(uint8_t index, bool clockwise)
+  
+OPTION: set ENCODER_DEFAULTACTIONS_INDEX in config.h to the encoder number if the encoder is not index 0  -- set to 1 for top right encoder
+
+TD_LSFT_CAPSLOCK_ENABLE = yes
+- This will enable double tap on Left Shift to toggle CAPSLOCK
+-   KC_LSFTCAPS to bind to left Shift to enable feature
+-   KC_LSFTCAPSWIN does the same thing but will not turn on CAPS when Win Lkey is disabled
+    
+INVERT_NUMLOCK_INDICATOR
+- inverts the Num lock indicator, LED is on when num lock is off
+
+ALTTAB_SCROLL_ENABLE
+- When ENCODER_DEFAULTACTIONS_ENABLE = yes, 
+    Enables Alt-Tab scrolling functions in default encoder, 
+    bind KS_TSTOG to a key to enable/disable Alt-Tab vs Volume control
+- When defining your own encoder functions use encoder_action_alttabscroll(bool clockwise) to assign the encodr action
+
+
+Layout
+![image](https://user-images.githubusercontent.com/71780717/128580303-5d660a5f-1420-4e38-b40a-212573496b1c.png)