Work in progress on numerical range tests.

change: make RoundTrip tests even easier to write
change: bring back default value in reader before throwing numeric parse exception
Float and double round-trip tests now working. Decimal still fails.

change: allow unsafe code in tests in order to do bit-level comparison of floating point results
change: reformat code for nasty style :-p
add: explicit method for writing floats, in round-trip format
fix: use round-trip format when writing doubles