* Expose unicode_saved_mods
* Add UNICODEMAP shift pair functionality and XS keycode
* Add XS to keycode reference documentation
* Pick pair index based on both Shift and Caps Lock state
* Add XS to Unicode feature docs
* Clean up process_unicode* headers
* Extract unicode_map index calculation into function
* Pick pair index as XOR rather than OR of Shift and Caps states
* unicode_input_start() has to be called before the unicode_map index is calculated
* Replace unicodemap_input_error() with more generic unicode_input_cancel()
* Replace register+tap+unregister with tap_code16(LCTL(LSFT(KC_U)))
* UNICODE_OSX_KEY → UNICODE_KEY_OSX, UNICODE_WINC_KEY → UNICODE_KEY_WINC
* Make keycode range checks more robust
* Fix keycode range checks for different input modes
* Add UNICODE_KEY_LNX, update docs
* QK_UNICODEMAP_SHIFT → QK_UNICODEMAP_PAIR
* XS → XP, update docs
* Tweak Unicode docs
* Use recently added MOD_MASK_SHIFT and IS_HOST_LED_ON helpers
* Update Unicode table in docs/keycodes.md
* Update Unicode docs per review comments
* Replace references to Mac OS X with macOS in Unicode docs
* As of v0.9.0, WinCompose supports all possible code points
* Expand descriptions in XP docs
* Update keycode table and cycling docs
* Further expand cycling docs
