Add *.pyc to .gitignore

Useful for sublime plugin development
Add links to key bindings to package settings menu.

Also, remove unnecessary keys  "caption" and "mnemonic".
Implement new API

* Add js_lint_folder and js_lint_containing_folder commands.
* Rename jslint to js_lint_file command.
* Add js_lint_exec helper command.
* Rename Default.sublime-commands to JSLint.sublime-commands as this is
the standard.
* Update context menu.
* Add menu item "JSLint Folder" to side bar context menu.
* Update sublime-commands.