reworked flow change function
This should have been it's own branch. I removed the useless pipe age field and replaced it with a design flow (as a percent of pipe-full). This gives a more accurate, although wholely unnessessary flow change percent. I really just wanted this code done for the next app (a manning's partially-filled pipe calculator). Due to the complexity of the new flow calculator, I broke out the flow change function into its own module. The next step is to modify the language to get rid of the 2/3 verbage and plug in the actual full percent.