Porting instructions

What changed?

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).

1. 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.

1. please use ring members (e.g. r->N) instead of (currRing specific) global variables (e.g. pVariables)