Move logic for printing usage to separate function.
Add skeleton for option parsing.
Write PNG to stdout.

Get rid of the ugly hardcoded "text.png" output file and just write the
PNG to stdout.  This is a sane default.
Add --output command-line option.

Allow an output file to be specified to override the default of writing
the PNG to stdout.
Handle input file more consistently.

Use "-" as the default input file and make the fopen() logic conditional
on having specified something other than this default.  This makes
the default case consistent with handling an input file set explicitly
to "-".
Require single geometry argument.

Accept a geometry specification on the command-line instead of separate
width and height arguments.
Use the MIT license.

Basically DWTFYW.