Introduce SpecFetcher proxy.

Based on jstrzibny's work.
Introduce Package proxy.
Introduce Format proxy.
RubyGems 2.0 compatibility.

Based on jstrzibny's work.
Fix -d option with RubyGems 2.0.

Based on jstrzibny's work.
Update documentation.

* Add package variable for template.
* Note that format is now deprecated.
Update templates to match the changes in source code.
Correctly return URLs for older releases of gems.

Interestingly, this bug went unnoticed for almost 5 years.
Fix source url for RubyGems 1.8 compatibility.
Drop support for RubyGems older than 1.0.0.

EPEL5 has RubyGems 1.2.0+ since 2009. So we can be reasonable sure that
nobody cares about older RubyGems.
Version bump to 0.9.0.
Behave better when no connection is available.
Remove superfluous string interpolation.
Unify error handlind.
Version bump to 0.9.1.
Fix release files encoding.

Apparently, release file is UTF-8 encoded (thank you Schrödinger's Cat).
Version bump to 0.9.2.