Support setting Authorization in prepare_request

I use pithub in some scripts, but I relied on prepare_request to provide the
token for auth. This worked for some requests, until I stumbled upon the
has_token problem.
v0.01018
Fix missing changes entry.
Replace JSON::Any with JSON
Merge pull request #150 from ghedo/master

Replace JSON::Any with JSON
Update Changes.
v0.01019

          - Replace JSON::Any with JSON (Alessandro Ghedini)