Added .ropeproject to .gitignore
Added new keyword argument to `slumber.API` perm_params.

`perm_params` is dictionary of params which will be merged with
request-specific params each time get, post, put, patch, delete is
called.

Use case is e.g. tastypie API key auth, where you instantiate
slumber.API with perm_params={"username": "my_username", "api_key": "my_api_key"}.