Some changes:

1) Included constants.h in all source files
2) Made it so that bool returning functions are an integer type for C if C++ is not in use
More improvements:

1) Stripped out some unnecessary includes
2) Each file now has appropriate includes for whichever ones are needed and no longer rely on headers being included with another include except for the *.cpp file relying on the associated *.h file for shared includes. I may change that later on, however.