Method set generation for Provider interface

[muvaf]

Signed-off-by: Muvaffak Onus onus.muvaffak@gmail.com

Description of your changes

Implements code generation for https://github.com/crossplaneio/crossplane-runtime/pull/93

Checklist

I have:

• [x] Run make reviewable to ensure this PR is ready for review.
• [x] Ensured this PR contains a neat, self documenting set of commits.

[muvaf]

@negz The PR I was waiting is merged and I confirmed that this PR does what's expected.