api: Implement the 'redraw:tabs' event
api: Implement the 'redraw:insert_line' event
api: Implement the 'redraw:delete_line' event
syntax: Store RGB color information in cterm attribute entries.

This is a temporary hack: When terminal dependencies are removed, only RGB will
be used to describe colors(terminal-specific UIs will translate RGB to terminal
color codes)
api: Implement the 'redraw:update_line' event
api: Implement the 'redraw:status_line' event
api: Implement the 'redraw:ruler' event
api: Implement the 'redraw_{fore,back}ground_color' events
api: Implement the 'redraw:layout' event
api: Implement the 'redraw:cursor' event
api: Implement the 'redraw:win_end' event
api: Implement vim_request_screen to force redraw events
api: Implement vim_command_output function

This function can be used by API clients to execute a command and capture the
output.
Use character offsets instead of byte offsets for attributes
Redraw when colorscheme changes
Fix attribute table lookup