Communication via HTTP

[nvcnvn]

With the pull request https://github.com/google/gops/pull/30 seem will be accepted I want to make it a step further by making the gops tool "speak" with agents via HTTP rather than reading each single by via TCP.

Benefit:

• More firewall friendly and save a port (in my work place 80 is always open)
• Easier to extend

I will happy to work on this if accepted.

[rakyll]

I would prefer to switch to HTTP, there are a few feature requests that require complex payloads and custom protocol on TCP is not the way to go :)