OmniDocs is a ST2/3 plugin for jumping to documentation for:
 -  selected symbols
- 
imported modules / API
 - 
language reference
 
Some languages are supported out-of-the-box but other can be added by customising the settings.
The basic usage is pressing F1 when needing help; a panel will be shown with the possible options:

Any contributions or suggestions are welcome at github.com/bordaigorl/sublime-omnidocs/issues