Log Message:
update to 2.2.0
changes:
-Bug fixes
-New functions mpfr_set_overflow, mpfr_set_underflow, mpfr_set_inexflag,
 mpfr_set_erangeflag, mpfr_set_nanflag, mpfr_erfc, mpfr_atan2, mpfr_pow_z,
 mpfr_subnormalize, mpfr_const_catalan, mpfr_sec, mpfr_csc, mpfr_cot,
 mpfr_root, mpfr_eint, mpfr_get_f, mpfr_sech, mpfr_csch, mpfr_coth,
 mpfr_lngamma
-New macro: MPFR_VERSION_STRING
-The exported MPFR variables have been removed from mpfr.h
-cleanup, speed improvement...