Merge pull request #5 from TheSquishyDitto/master

Fixed two minor errors that prevented compiling.
I just changed the header guards to match what we have been doing (FILE_INCLUDED instead of MARBALLS_FILE_H)
Changed the include guard to what we have been doing also added pfgen.h to marballs.h header file (global include)
Update pfgen.h
Finished Chapter 6

Corrected small typo in decimal_precision.h, Added spring, anchored
spring, bungee, buoyancy, and fake spring generators to pfgen.h and
implemented them in pfgen.cpp.
added pcontacts.h pcontacts.cpp plinks.h plinks.cpp
Update Version_History.txt
Update Version_History.txt
added October time sheet
Merge pull request #6 from sunworld23/master

Updated
Just cleaning up the time sheet
Left off on page 135, Chris is going to finish chapter 8.
Update October_Time_Sheet.txt
Update October_Time_Sheet.txt
Chris fixed some errors in chapter 7 and finished chapter 8. We need to debug before continuing.
Fixed a few things
This is the correct push, updated the wrong files at first.
Merge branch 'master' of https://github.com/theonejcv/Marballs
Delete October_Time_Sheet.txt
Delete September_Time_Sheet.txt