Adding functionality to connect mne rt-client to fieldtrip rt-client.

This addresses https://github.com/mne-tools/mne-python/issues/982. I have modified the original C code by @LauriParkkonen to add the capability for emulating from a file. The compiled binary (64-bit, CentOS) in this folder http://neuro.hut.fi/~mainak/neuromag2ft-2.0.0.zip should hopefully work good as the server. Something like this worked on my machine:

`$ neuromag2ft-2.0.0/bin/x86_64-pc-linux-gnu/neuromag2ft --file mne-python/examples/MNE-sample-data/MEG/sample/sample_audvis_raw.fif`

TODO
- [x] Fix camel case in function names.
- [x] Fix docstrings in code by S. Klanke to comply MNE-Python conventions.
- [x] Add threading like in the `RtClient` class using callbacks etc.
- [x] Use WAIT_DAT instead of GET_DAT to improve timing

cc @LauriParkkonen @mluessi @Eric89GXL @agramfort