Update script as per Code Review

As per [code review][review]:

- Update all references using unary operators to extended test command
  syntax
- Update all unnecessary extended test commands and subshell comparisons
  for proper syntax
- Update exit codes to use proper distinction between various types of
  errors
- Update all flags within for loop
- Update all printf or formatted strings to use a format specifier and
  double quotes

[review]: http://codereview.stackexchange.com/q/48050/16370

Issue: #3
Update man page for proper exit codes

Issue: #3
Update wiki