Fix bugs when converting gmp to float

The ``float_`` intrinsic was not overloaded for GMP.

Thanks to g webb for spotting the bug!
Merge pull request #174 from serge-sans-paille/fix-long-to-float-conversion

Fix bugs when converting gmp to float
Portable specialization of boost::hash_value

Fix #175
Merge pull request #177 from serge-sans-paille/boost-hash-value-fix

Portable specialization of boost::hash_value
Merge remote-tracking branch 'serge/master' into devel
Fix, add generator