Add the ability to use a custom serializer for storing the object in the database
Update tests for differences in Ruby versions
Merge remote-tracking branch 'bradleypriest/master'

Conflicts:
	lib/paper_trail/has_paper_trail.rb
	lib/paper_trail/version.rb
Update CHANGELOG.
Update contributors.
Bump to 2.7.0
Update README.
Re-ordering CHANGELOG to be in order of pull requests made.  Slight reword of impact resulting from #164.
Making it so that the paper_trail initializer for the dummy app is in the dummy app's config/initializers directory so that it mimics the behavior of the rails app when the console is run against it.