Two command-line tools: oauth-generate-signature and oauth-generate-header

[jdormit]

This adds two command-line tools, generate-oauth-signature and generate-oauth-header. It also adds documentation on both in the README. They do pretty much what you'd expect, both writing their output to stdout. Two new dependencies are introduced: commander.js to handle option and argument parsing and chalk to handle colored terminal output.

[bettiolo]

Thank you very much for the PR!

It would be great if you could add some tests as well.
Would you be able to do so?

The documentation looks great!

[jdormit]

Sure thing - I won't be able to until sometime next week, but as soon as I do I'll let you know.

[ronkorving]

Nice addition! I think it would be pretty cool to add a (verbose) -v to generate-oauth-signature that would also output the base string, etc, so it can be used as a debugging tool to compare against other solutions.