fixes colspan width calculations, e.g. #407
A couple minor dev toolchain tweaks

* Remove RDoc task now that we're using YARD
* Make gemfile read from gemspec for dependencies
Merge pull request #620 from prawnpdf/colspan-fixes

Colspan fixes
Add failing test for #612
Clarify documentation in response to #597
Extract YARD options into .yardoc

This is required for YARD to build docs on gem install
Add failing test for #603
Merge pull request #623 from prawnpdf/yardoc

Extract YARD options into .yardoc
Added liceses to the gemspec
Merge pull request #624 from prawnpdf/licenses

Added liceses to the gemspec
Rename LICENSE to RUBY in gemspec
Add .yardops back
Remover reference to prawn-fast-png because it is broken. Will update with prawn-gmagick once we prove it's stable
Get rid of all internal uses of require to load prawn source code, replacing them with require_relative calls.
table column width was not correctly calculated (in certain circumstances) - fixes #628
improving manual / metadata example
manual - improved wording for metadata example
Merge pull request #630 from prawnpdf/manual_metadata_example

improving manual / metadata example
Dup the previous state's dash attribute when copying
Ensure that the color_space and dash attributes are properly copied when using dup/clone to copy a graphic state