Support parameter names with +, with extra allowed characters

[czechboy0]

Support parameter names with +, with extra allowed characters.

Some OpenAPI documents use e.g. /foo/{+bar}, which means the bar variable has a larged allowed character set.

But the generator today rejects it because it looks for the parameter named exactly +bar, and that's not found.

[czechboy0]

If we can exclude / from the allowed characters, so that one path component can't suddenly become multiple, this shouldn't be too difficult. Will just require adapting the URIEncoder/Decoder, and passing along an extra flag.