Update gogoclip.hpp: change functions

Remove the "GetPreviousInputP" function as having it split into the two
new functions makes more sense.
Update util.hpp
Update gogocli.cpp
Update gogocli.cpp: big cosmetic change

Restructures the code so that it is more easily read and/or worked with.
Only functional changes are that the Add() and Remove() functions now
return gogo::error upon any errors and 0 upon success, like Call().
Update gogocli.cpp

These two cosmetic changes were supposed to be in the previous commit.