Update highlighting to exclude syn-keyword options
Update highlighting to exclude syn-keyword options

If any highlight keywords have the same name as a :syntax-keyword
option (i.e. "Contains"), an error is raised.

This commit excludes these keywords from :syntax-keyword groups, and
instead calls matchadd() on them individually - cleaning up before
subsequent highlighting with matchdelete().

OmniSharp/omnisharp-vim,OmniSharp/omnisharp-vim,OmniSharp/omnisharp-vim