Remove the proxy API (closes #43)

[tarcieri]

See #43

If the proxy API isn't working it should be removed. We should either fix it or remove it.

If it's removed it can be placed onto a branch where someone can fix it later if they so desire.

[ixti]

After moving away from Net::HTTP we simply have NO proxy API. It's possible to specify proxy, but that option is simply not used anywhere. So I would propose to remove that option, remove proxy references in README and close tickets. Later if someone would love to hook up proxy support, he will be able to start from scratch. No need to keep current stuff as it's worthless at this state.

[tarcieri]

Seems good