FD Performance Tuning

@Myoldmopar @mjwitte @amirroth @lgentile
This is a semi-major refactoring to address performance of FD cases that were running much slower than EnergyPlus 8.1 (Fortran). For the test case tuned against the performance should now be ~20% faster than 8.1.

Expressions were reorganized to reduce op counts, resulting in some small numerical changes. My test suite passes for these mods.