Add version handling

Give ability to grape-swagger to distinguish  and handle multiple grape api versions.

Repurposing api_version to pull desired version from query string.
Only routes for the specified version will be returned

Possible related issues:
[141](https://github.com/tim-vandecasteele/grape-swagger/issues/141)
[146](https://github.com/tim-vandecasteele/grape-swagger/issues/146)
[38](https://github.com/tim-vandecasteele/grape-swagger/issues/38)