Added test suites

Added a few tests that both test the parsers as well as the `gen_lockstep` behaviour.

Also removed the `rebar` binary. It was outdated. I expect the developer to either have a local `rebar` installed or copy one in herself which is why the `rebar` is now added to `.gitignore`.

There is one code change in `gen_lockstep.erl` to make it possible to configure the idle timeout.

I found a few possible bugs that might be important enough to be tackled later on:

* `gen_lockstep` server locks up if no body is sent just waiting for incoming data;
* `gen_lockstep` server locks up if the remote HTTP server accepts the connection but sends no data back;

Both of these bugs are there because the timeout is only set after successful (or unsuccessful) parsing of data - if there is no data no timeout is set.