- Localize vars
- Add const
- Simplify status reporting and status var
- Free any malloced memory in the OOM case
- Remove unnecessary goto
- Use stderr for error message

Thanks to Kurt Schwehr for finding this

Found by UBSan

C99 is now required.  Therefore HAVE_STDINT_H is no longer necessary.

encode_accessors.h: include "config.h" to allow header to stand alone

Minor cleanup of fuzz_target.cc

codespell: dependance  ==> dependence

Some compilers do header precompilation and this requires that each
header can stand alone.  Including config.h sets HAVE_STDINT_H.

- Include What You Use (IWYU) - add cstddef
- Convert to C++ includes of C headers
- Localize vars
- Combine definition and initialization of dest
- Convert C cast to C++ cast
- Remove unused source var

Use Cmake for fuzzing.

Some files, e.g. encode_accessors.c, use loop initial declarations
that are only allowed in C99 mode. Newer compilers enable that mode
automatically, but olders might fail. CMAKE_C_STANDARD got add in
CMake-3.1, so let's increase the minimal version by 0.1.
Signed-off-by: Christoph Junghans <junghans@votca.org>