Function cleanup

* Instead of counting ID length at the same time as counting size length, they have been split into two different goroutines.
* The scanDirectory function has been made easier to read by the addition of a checkForHiddenFiles function.
* getUserList and getGroupList have had their number of steps reduced. Instead of temporarily storing the uid/gid in a variable, it is appended directly to the list.
* printLongModeFile has been shortened by the addition of a checkIfSymlink function.