pass version manually

[FrancescoCioria]

requirements

Users should be able to pass the version they want to release manually.
This is useful in those cases where the automatic breaking/minor detector fails for some reason (like if you want to release a rc or a beta).

The version should be passed as main argument to smooth-release:

smooth-release v4.5.6

specs

{optional: describe technical specs to implement this feature, if not obvious}

misc

{optional: other useful info}