Improve Ansi-C implementation via SonarQube analisis

Where appropriate, cleanup the implementation of Mpm code base, which shows legacy of old ways to do things. When modern C/C++ compilers and project editing environments signal casting warnings, fix these, so end-to-end compilation on cross-platform system are silent (no compilation noise!).

Recently, this project has been established with a free code-analisis service by SonarQube (SQ) here: https://sonarcloud.io/dashboard?id=bits4fun_mpm

which is linked to the project on gitlab.