Change program instrumentation to clang libtooling
Currently, we use pycparser for C parsing and instrumentation for coverage measurement. This misses support for (at least) GCC extensions (current handling) and variadic functions (#26 (closed)).
To improve on this, our only choice seems to be the switch to another parser. Clang libtooling seems to be a viable and sustainable solution, as it is based on the full-fledged clang compiler. This may also speed up parsing (#25 (closed)) and allow support for highly-nested programs (#24 (closed))
The new implementation should provide at least the same functionality as our current solution