start work on pushing fill attributes down to subtrees with only loops

See diagrams/diagrams-svg#43.
implement splitFills for case of style node
finish implementing splitFills: RPrim case
D.Attributes: fix warnings
D.Attributes: clarify comments on splitFills
Exclude joins in offsets on close segments (Fixes #160).
finish implementing splitFills (with tests).
CHANGES for 1.1
require diagrams-core-1.1
Added `frame` section
edit `frame` description
update tested-with field
update copyright years
fix doc for === and |||
Merge pull request #164 from denys-duchier/doc-fix

fix doc for === and |||
add Denys to contributors list
add GHC 7.8.1 to tested-with field
Merge pull request #161 from diagrams/split-fills

Move FillColor Attributes to subtrees with only Loops
Wall: remove extra imports
initial commit