Documented the new fmpz_single.c file.
Documented the new fmpz_single.c file.

fredrik-johansson/flint2,fredrik-johansson/flint2,jpflori/flint2,jpflori/flint2,dsroche/flint2,wbhart/flint2,dsroche/flint2,dsroche/flint2,dsroche/flint2,wbhart/flint2,wbhart/flint2,jpflori/flint2,fredrik-johansson/flint2,jpflori/flint2