Significant improvements in plumedcheck

- Vim syntax for the awk file
- Some information is given once per file now.
- Registration of vessels and metrics is also logged.
- Check that .h files do not include:
  * inc files (they are temporary)
  *  external .h file (they might be not available when using plumed library).
The latter is only notified now, since it must be accepted for mpi.h
- Separately store documented actions/cltools/other.
- Check that module type is correct.
- Extensive doc for each check added.