Use David M. Gay's STRTOD instead of system specific atof().
Add boilerplate to reb-dtoa.h
This is a major change improving accuracy and compatibility of LOAD DECIMAL! across platforms.
Also, improves accuracy and compatibility of MONEY! to DECIMAL! conversions across platforms.
Undefine strtod to suppress redefinition compiler warning.
Merge pull request #144 from ladislav/STRTOD

Use David M. Gay's STRTOD instead of system specific atof().