cmus 2.6.0

Signed-off-by: Gregory Petrosyan <gregory.petrosyan@gmail.com>
Add mouse support

Add option mouse=true/false

Add bind keys:
- mlb_click,
- mlb_click_selected,
- mrb_click,
- mrb_click_selected,
- mouse_scroll_up,
- mouse_scroll_down
Add conditionals to format strings
Add format_treewin, format_treewin_artist, format_trackwin_album
Fix expr_free(NULL) and long format options
added playcount field
incrementing play count for tracks
play count being saved to cache
unheard filter
play_count filter