Issue #39 - Support for stand-alone comments

Issue #39 - Support for stand-alone comments
Add missing background and border properties and constants

Issue #27 - Add missing background and border properties and constants
Added missing Text Decoration properties and constants

Issue #31 - CSS Text Decoration Module Level 3

Added missing properties and constants
Issue #35 - Reviewed Code Critics
Issue #40 - Gradient Support

Issue #40 - Gradient Support

Addes support for linear-gradient(), radial-gradient(),
repeating-linear-gradient(), repeating-radial-gradient() and some
constants
Release 1.3.0

Updated metacello configs.
Merge pull request #41 from gcotelli/master

Release 1.3.0