remove obsolete URI.escape and implement by ourselves
fix warnings
Properly escape values in OAuth header, see:

http://oauth.net/core/1.0a/#auth_header

> Parameter names and values are encoded per Parameter Encoding.

Implement godfat/rest-more#6

Note that before doing this, Twitter and LinkedIn do accept
values which are not escaped. However, we're still trying our best to
follow the spec, of course.