Fixed several problems with mv.go

* Converted the if/else checks for file argument count into a switch.
* Moved the switch to it's own function, named argumentCheck.
* Fixed a case that was not working and added an additonal case.
* Changed the names of the force flags so that they are easier to read.
* Added check at the beginning of the program to set forceEnabled to true if the long version is used, which removes the need for redundantly checking both flags.
* The input function now works, when before it did not.
* Also converted the initial if/else in mover into a switch.
* In mover, check to see if the original file exists before checking for the destination
* In mover, remove the redundant case at the end and merge it with default.
* Added a few comments to the code.