Allow urls to end in slash

[BSVogler]

Prevents double slash in url.

Implements support for optional port in url #76

[ruscoder]

@BSVogler I reviewed the issue and PR again. It seems the logic of adding the default port can be merged. But let's move it to a separate function and add behavior for HTTP (80 port) either. And finally, cover this function with unit tests to make sure that it works correctly for all options.