Accessor methods on HttpUrl.Builder

[JakeWharton]

Enough to fulfill Retrofit's need of doing path replacement with proper encoding on an instance.

[swankjesse]

After further investigation it looks like it’s difficult to get an API that works the way Retrofit wants. In particular a path like @Get("/{foo}{bar}") might be problematic if foo is encoded already and bar is not. That sends us down the ugly road of offering one-off encoding and decoding methods, which I’m not eager to do.

No action to take at this time.