- resolve name space clash between PFFT_FLOAT (input data type) and PFFT_SINGLE (build system variable)
- rename PFFT_SINGLE, PFFT_LDOUBLE to PFFT_PREC_SINGLE, PFFT_PREC_LDOUBLE
- introduce PFFT_PREC_DOUBLE for the default case
- extend getargs to long double
- use strtol, strtof, ... instead of atoi, atof, ...
update F03 interface