Start to move files below src

Prodded by @hellais.
Remove now-unused gen_cxx neubot.hh
Actually ext belongs to src
Add a new copy of http-parser below src/ext

Apparently, my version of Ubuntu does not implement the
git submodule deinit command; being lazy, I'll delay such
command for when I'm in a system with deinit.
Actually echo.c belongs to Neubot
Add common and net include.am
Add Makefile.am prototype to be worked in tree
Delete http-parser submodule.
Add include.am for src/ext/, src/ and src/neubot/
Rename all includes to point to new header locations.
Use autotools step 1

The old configure now is config.local and is executed at the
end of the configure process, after config.status.

The new configure.ac allows one to specify the place in which
libevent is installed, using --with-libevent=foo.

Add empty directory, m4, in which m4 files are saved.
Merge remote-tracking branch 'hellais/big-rename' into big-rename
Use autotools step 2

Roll out a working set of Makefile.am:s and, while there, fix
the sources so that they actually compile.

This quest is not finished yet, more to come.
configure.ac: make sure we run config.local
Teach config.local to autogen src/ight_wrappers.h
src/include.am: also install headers
Send libneubot_python to the attic

It was not the way to go, and was on my way while moving
from libneubot to libight.
Be tidy, move scripts below the scripts directory
Use automake also in the unit test
README.md: update build instructions for autotools

The remainder of the file is unchanged. Of course, more editing
is needed to s/libneubot/libight/, but this thing will be done
later and in another branch, to avoid to heap too many diffs to
the current branch.