Remove trailing whitespace in lib/ and spec/
Move Prawn::Core into PDF namespace.

This commit does not address the circular dependencies that exist between
Prawn and its core API, but it does pass the tests and generate the manual!
Move PDF::* to PDF::Core::*
Move PDF::Text into PDF::Core::Text
Remove references to Prawn constant within PDF::Core namespace
Make it possible for us to add failing tests for bugs without breaking full suite run.
Set version number to 0.13.0, update gemspec
Make sure to require pathname
Increase number of iterations in PNG benchmark
Increment benchmark iterations again
Add benchmark for PNG object allocation
Merge branch 'master' of github.com:prawnpdf/prawn
Add acceptance test (manual verify) + tweak benchmark
Make transparency obvious in acceptance test
Remove duplicate file
Bump to 0.14.0 to reflect divergence from stable
Add gem version badge
Alternative PNG alpha-channel extraction

According to PNG spec filtering happens on a per-byte basis and uses
corresponding bytes from other pixels. This means that we don't have to actually
unfilter all the data. Instead it's possible to split pixel data into planes.

A few points to note:

* Filters are reused from original image
* Resulting opaque PNG uses the same filtered data
* Resulting mask PNG image uses the same filteres data
* Both resulting images are valid PNG images
* All the unfiltering masth is skipped which results in great boosts