Add vspec#pretty_string
Add tests on vspec#pretty_string
Implement the ideal vspec#pretty_string
Add tests on special characters in faield tests
Use vspec#pretty_string
Merge branch 'show-decodable-strings-in-failure-messages'

Close gh-39.
Add release notes on 1.3.0
Bump up version to 1.3.0
Merge branch 'prepare-for-1.3.0'