Refactor matcher_spec.
Refactor matcher_spec.

- Use a helper method to create the matchers, rather than
  `Matcher.new` + `for_expected`. I plan to rewrite the
  implementation of `Matcher` in a way that will require it
  to be instantiated differently and I having this helper
  method gives us only one place to update.
- Prefer `let` to `before(:each)` ivars.
- Define the module inline as a local; this avoids the need
  for the awkward `m = mod`.

jamelablack/rspec-expectations,zsyed91/rspec-expectations,danielfone/rspec-expectations,edwardpark/rspec-expectations,sferik/rspec-expectations,chrisarcand/rspec-expectations,yaoshipu/rspec-expectations,jdax/rspec-expectations,jamelablack/rspec-expectations,zsyed91/rspec-expectations,dg-ratiodata/rspec-expectations,jasonkarns/rspec-expectations,dg-ratiodata/rspec-expectations,unmanbearpig/rspec-expectations,emilyforst/rspec-expectations,jdax/rspec-expectations,danielfone/rspec-expectations,bjpcjp/rspec-expectations,emilyforst/rspec-expectations,AEgan/rspec-expectations,chrisarcand/rspec-expectations,maclover7/rspec-expectations,AEgan/rspec-expectations,edwardpark/rspec-expectations,yaoshipu/rspec-expectations,bjpcjp/rspec-expectations,maclover7/rspec-expectations,rspec/rspec-expectations,h4ck3rm1k3/rspec-expectations,sferik/rspec-expectations,h4ck3rm1k3/rspec-expectations,unmanbearpig/rspec-expectations,alexaltair/rspec-expectations,jasonkarns/rspec-expectations,alexaltair/rspec-expectations,rspec/rspec-expectations