Modified descriptions on the bundler utilities that allow extra options to clarify that they are expected to be added after the command name.
Merge pull request #2904 from aitor/master

Excplit order of `options` to gem command descriptions.
Added the --ext option to the gem command. This generates a skeleton for C extensions.
Git ignore build artifacts.
Throw an error whenever a gem name does not conform to the C extension naming guidelines.
Fixed failure in bundle gem command spec due to extra newline added in #2891