Set comment of output image to null

- Remove comment for output image (== thumbnail) by default, uses
  epeg_comment_set from the epeg library
Merge branch 'feature-remove-thumbnail-comment' into v0.1.1
Adds chainable quality method

- Example: Epeg::Image.open("/some-image.jpg").quality(50).to_blob
Merge branch 'feature-chainable-quality-method' into v0.1.1
Add require directive to installation paragraph
Merge branch 'fix-readme' into v0.1.1
Remove unused attributes

- @file_path which is not used anywhere at the moment
Merge branch 'fix-remove-unused-attributes' into v0.1.1
Fix Epeg::Image#resize_to_fill and Epeg::Image#resize_to_fit

- Fix typos and incorrect math causing wrong image dimensions
- Add better jpeg for testing (einstein.jpg)
Merge branch 'fix-resize-to-fill-or-fit' into v0.1.1
Change rake-compiler from runtime to development dependency
version bump