Small addition in documentation
Provide a custom inspect method

Image#inspect now returns a shorter string for inspection,
in particular the pixel data is no longer included.
Remove :nodoc: tag from constants
Remove :nodoc: tag from private methods
Do not show documentation for helper classes

Mark Converter and Parser class with :nodoc: tag.
Add @private tag for YARD documentation
Add .yardopts file
Remove PNM magic number details from documentation
Release 0.3.3
Reintroduce :nodoc: tags for private methods
Allow string values for the type option in Image.new
Update Ruby versions in README
Release 0.3.4