Update changelog and add entry for v3.1.2

Update CHANGELOG for v3.1.1

Additional tests for invalid recorder mode and ModeRecordOnly

Add IsRecording() and IsNewCassette() methods

Update badge links for build status and documentation

Update package imports to use gopkg.in/dnaeon/go-vcr.v2

Update test cassettes

Update README

Commit v2 structure

Merge pull request dnaeon#61 from Blesmol/update_yaml

Update gopkg.in/yaml.v2 from v2.2.1 to v2.2.8