Rewrite vimux using VimL.

This commit also drops the deprecated functions and removes some rarely used
functions such as VimuxClosePanes.
Update help docs for 1.0.0.
Fix typo in 1.0.0 docs.
Only escale double quotes. Thanks @pgr0ss
Merge branch '1.0.0rc1'

Conflicts:
	plugin/vimux.vim