Support using Ref in FunctionName

[youngchen7]

This change adds the ability to use !Ref in FunctionName.

We plan on using this to during deployment to run a release task that pushes lambda to staging vs production lambda functions depending on environment variable config.

[youngchen7]

@adrianpraja let me know how this looks! 😄

[adrianpraja]

Hi @youngchen7,

this repository code is old and unmaintained I had no idea people still using it or that if it even works

I'll take a look at your PR in the weekend, let you know if I have questions, merge/release is not.

Adrian