Pass blocks through with `MR::Factory.new`

This updates `MR::Factory.new` to properly pass blocks through
to the record and model factory. This is needed so that default
args can be provided using this macro. This also adds a test to
ensure this behavior works.
Merge pull request #77 from redding/jcr-pass-blocks-through-with-factory

Pass blocks through with `MR::Factory.new`