renamed RevisionMetaInfo class attribute _revisionmetainfo
renamed _revisionmetainfo class attribute as _concurrencymeta
renamed RevisionMetaInfo as ConcurrencyOptions
per model ConcurrencyMeta
rename ConcurrencyOptions.field as _field
rename ConcurrencyOptions.versioned_save as _versioned_save
rename ConcurrencyOptions.manually as _manually
add test for ConcurrencyMeta
update Makefile to print python version
add tox to requirements.pip
Merge branch 'feature/custom_revisionmetainfo' into develop