MD Uebung files

This is a simple 2-dimensional MD program, but it is not complete. As homework, you have to write the missing parts in md.c.

This Uebung began with code from Marco Matthies and Nils Petersen. In June 2022, I moved executable code out of rvec.h. As a matter of style, one should never have code or anything that allocates space in .h files.

I removed some unnecessary lines from the Makefile.

BUGS

If you compile with -Wall, there will be some warnings about unused variables. These are not a problem. This is an assignment in which one should write code that uses these variables.