First iteration of the HTTP client for cpp-netlib v1.0.0a

What is there to say? Too much for this description. Just:

1. I not only updated the code, I updated some of the configuration too.
2. The HTTP client is far from feature complete at this stage, but I am not too worried about that yet
  a. byte_source is not implemented, therefore no request body yet
  b. client_options and request_options need work
  c. No SSL for now
3. The implementation diverges from the design doc: https://docs.google.com/document/d/1jUJxs99bcbxAFIWn4Slm8JIMMmrtKc3jwhBz6Da05Lk/edit#heading=h.2sedacots1jw we should discuss this
4. I added a .travis.yml for CI: everything compiles, all tests pass for all build configurations
5. We need to come up with a way of merging what we can from 0.11-devel into master
6. Source documentation is incomplete
7. Run `make doc` to generate the class documentation (make sure doxygen is installed)
8. the best thing to do first is to look at the tests, and at the simple examples (under the contrib folder)

And  many other things that we can discuss when you have time to look at this.