What has been changed in Singular 4

1. lots of stuff moved in the headers, which messes up the includes. This should be fixed already. If there is still a problem look in test.cc for the correct includes.
2. coefficients were separated from polynomial rings.
   • There is a new type coeffs.
   • Operations on coeffs are done by n_* functions, where coeffs is the last argument (consider it as the context storing information on the coefficient domain).
   • Functions like nAdd(a, b) become n_Add(a, b, r).
3. new arithmetic functions.
   • Same as the previous.
   • Arithmetic is done with p_* functions, which take a ring as the last argument.
   • The use of the global variable currRing is discouraged.
4. please use ring methods (e.g. rVar(r)) instead of (currRing specific) global variables (e.g. pVariables)