Remove wrappers from C++ to C and Python

The wrappers from C++ to C and Python were added to LibNeubot following
this rationale:

1) LibNeubot was to be written in C++ for SWIG to generate more
   easily usable NDK/JNI code;

2) The C interface was helpful to cherry-pick functions from Python
   using ctypes and to create a nice Python interface around the rought
   edges of the ctypes interface. In turn, this was because LibNeubot
   was to be used both for mobile and Neubot for PC.

After the discussion with @hellais that led to Libight, the scope was
narrowed to include only 1), because Libight is meant to support Neubot
and OONI on mobile platforms only.

Therefore (and, also, because the wrappers are on my way now that I am
working on a fully C++ poller that uses std::function and other C++11
goodies), I suggest that we remove the `optional complexity` represented
by 2) to develop more quickly.

In fact, if 2) is not a Libight objective, my time is better spent working
on the C++ core rather than working to keep 2) up to date.

I tested this change by rebuilding everything as in `make distclean;
autoreconf -i; ./configure; make V=0 check', without breakages or new
warnings.

I am aware that this diff removes some Python based tests, but C++ tests
are to be written in any case (I'd rather do testing of the C++ core than
do testing of the Python wrapper of the C wrapper of the core itself).
README.md: stop mentioning Python

Python was needed by scripts/gen_*, which were removed.
Axe more LibNeubot-specific stuff

The src/neubot directory contained only stuff that I used to
run the current version of Neubot using `ctypes` to load code
from libneubot.so.

There is no need to keep this code in Libight.

As a side effect, src/ight_wrappers.cpp can now go as well.

Also, remove dead prototypes from src/ight_wrappers.h.
Stop gitignoring things we don't autogen anymore
Gitignore the `autoreconf -i` artifacts
Gitignore the `./configure` artifacts
Gitignore stuff generated at compile time
.gitignore: test/echo_client2 is not deleted in this branch
common/poller.c: remove the obsolete defer_{read,write}() API

These two functions were used in one of my earliest attempts
to use a libevent-based core for Neubot.

They were not used anymore in LibNeubot (and I wanted to delete
them), so I feel obliged to remove them from Libight.

No breakages or new warnings by rebuilding all on MacOSX.
common/poller.c: remove the obsolete resolve() API

This API was used to experiment with Neubot, but it was scheduled
for removal from LibNeubot.

So, let's just remove it.

After this change, the Poller is small enough that the next step
can be to rewrite it using C++11.

As before, I verified that everything still builds smoothly.
Switch to the BSD license

This commit switches to the BSD license all the files that
are not touched by other pending pull requests (particularly
by #6 that, if accepted, removes a number of files).

Depending on #6 destiny, another commit to switch the remainder
of the tree will or will not follow.
Make the LICENSE more community friendly

The formulation of the license with 'each severally entitled'
works best if only Arturo and I are authors, and we plan to
receive no contributions from other people.

However, IMHO such sentence -- which implements disjoint
ownership -- also discourage contributions.

On the one hand, it is not common to see such sentence into the
license of a software. If it is strange, it raises eyebrows.
If it is not smooth, it is do-something-else.

On the other hand, the community should based on a pact by which
contributors can be sure that they contributed to a commons put
under the BSD license. To implement this, shared property (rather
than disjoint property) is needed.

So, I removed the disjoint property sentence and I extended
the copyright to include all the contributors.
Merge pull request #8 from bassosimone/switch-to-BSD-license-lite

Switch to the BSD license
Merge pull request #7 from bassosimone/gitignore-more-stuff

Gitignore more stuff
Merge pull request #6 from bassosimone/zap-libneubot-specific-stuff

Remove LibNeubot-specific stuff not relevant to Libight
Add note about initializing submodules.
Minimal rewrite of poller.c in C++
poller.cpp: use modern libevent API for evsignal
common/poller.cpp: simplify IghtEvent implementation
common/poller.cpp: remove unused headers