Add function to print version number in mkicon
Rephrase inline documentation in mkicon
Add standard command-line options to mkicon

The absolute minimum command-line arguments every application should
accept are:

* --help: print a short help message on basic usage
* --version: print the version of the application
Re-enable argument parsing capabilities

Argument parsing was temporarily disabled to implement the previous
commit.  To re-enable it, the arguments have to be distinguished and
processed by the *) case within the while loop.

The distinction of the input file and background color arguments is
determined by checking if a file exists, and setting variables
accordingly.
Add option to specify output location for mkicon

By specifying an output location, the mkicon script can be used by
automation tools like GNU Make or Grunt more conveniently.
Update help message in mkicon

List new command-line options and add reference to further
documentation.
Fix typo in startup image processor of mkicon

The present code was copy-and-pasted as-is and as a result, it contains
unrecognized characters by ImageMagick.  Replacing the characters re-
enables startup image generation.
Generate proportional banners in mkicon

Banners are images that have a centered icon image on a predefined
background color.  The centered icon image dimension is determined
by the narrow side of the image (the narrow side of the image is
divided by 1.6).  Since the orientation of banners can be portrait or
landscape, it is essential to detect the orientation of the output
image and adjust the centered icon image dimensions accordingly.
Fix whitespace issues in mkicon