changed main.cc file back (+2 squashed commits)
Squashed commits:
[bf6630c] Added some Doxygen comments to specify what the variables mean
[8d501e6] Changed main function to require specific number of command line arguments
collision.cc, working on
finished collision.cc
changed comments in collision.cc
fixed greater than
test
test
semi-implicit (symplectic) Euler added.  Very similar to Euler
removed unnecessary file
Delete new.txt
trying to make test
working on tests mroe
trying to incorporate extra-Newtonian forces
modify additional force implementation
add a simple test for additional force
delete orphans