Don't sanitize official plugin names, only g:installed_{plugin}

Resolves #55.
Inline function call for g:installed_{PLUGIN}
Merge branch 'master' of github.com:google/maktaba into no_sanitize
Bump version to 1.2.2
Merge pull request #57 from google/no_sanitize

Don't sanitize official plugin names, only g:installed_{plugin}