Simplify argument processing while loop
Check for dependencies on startup

Dependency checking ensures the application does not fail during
execution due to missing software.
Bump up version number of mkicon to 0.3
Shorten if-then clauses in mkicon

Always have a unified coding style within a project.
Create output dir for mkicon if it doesn't exist
Add trailing slash to output dir of mkicon

Due to the structure of the code, it is essential the output directory
has a trailing slash at the end of the argument.  Adding it
automatically ensures we don't run into issues considering this.
Add option for setting file prefix in mkicon
Make mkicon long options w/ args more standardish

Command-line double-dash (long) options usually are followed by equals
sign when passing arguments to them.  The script now follows this
convention with long options, while short option function normally
(the arguments are passed by leaving a space between the option and the
argument).
Add whitespace between case patterns in mkicon