API: Refactor: Rename find_{buffer,window,tabpage}

They were renamed to find_{buffer,window,tabpage}_by_handle to avoid conflicts
with existing functions of the same name.
Build: Fix error in dispatch generator for functions with channel_id
API: Refactor: Change type of event data to `Object` from `typval_T`
API: Refactor: Enable usage of Arrays and Dictionaries as [k]vectors

- Rename a/n/m to items/size/capactity in kvec.h
- Add capactity field to Arrays/Dictionaries
API: Refactor: Add helper macros for dealing with API type casts
API: Events: Implement the 'redraw:tabs' event
API: Events: Implement the 'redraw:insert_line' event
API: Events: Implement the 'redraw:delete_line' event
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: Events: Implement the 'redraw:update_line' event
API: Events: Implement the 'redraw:status_line' event
API: Events: Implement the 'redraw:ruler' event
API: Events: Implement the 'redraw:cursor' event
API: Implement vim_redraw_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.
Temporarily change python-client branch