Add fparser auto-differentiation module
Fix copy-on-write for AD subclass objects.
add missing include
add abs(), log2() and log10()
more trig funcs and decompose some multiops
being more explicit about Value_t, cleanup, add opcodes
cNop is only defined when the optimizer is enabled
protect more undefined symbols, start work on cFetch
add float based instantiation
add cRSqrt and cCbrt, rm cLog2by
update instantiation.
add helper function to test if function is == 0