add support for versioning using the 'Accept-Version' header
add documentation for :accept_version_header versioning strategy
Merge pull request #403 from politician/feature/support-accept-version-header

add support for versioning using the 'Accept-Version' header
Update README.md

update grape-entity URLs
Merge pull request #405 from ngpestelos/patch-1

Update README.md
Update CHANGELOG.md
Fix #407: specifying 'default_format' will also set the default POST/PUT data parser to the given format.