Module#prepend is public in Ruby 2.1
Merge pull request #91 from benlangfeld/mod_prepend_support_detection

Ruby 2.1 Module#prepend isn't private
fixup changelog for #91
Rename MethodSignatureVerifier to StrictSignatureVerifier, and add
LooseSignatureVerifier beside it to handle verifying with matchers.

I intend to use this in mocks to allow matchers to be used for keyword
arguments.