Add support for parameterized builds

Noticed that the build() method for a job did not work with parameterized builds (Both no way to pass in parameters, and would hit an incorrect endpoint anyways).

Added a new endpoint, and a new method to be used when a build is set to build with parameters.

Also updated the .gitignore to ignore .gem files and the .gemspec to point at README.md instead of README so that it would build the gem properly and not complain of a missing file.