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
Change return value of format_print
Add maxdate and daterange format options (for albums)
Add documentation
small fixes
Add %= support to format_trackwin_album
Simplify daterange
Remove daterange