Merge pull request #261 from Coeuvre/master

Repaired test cases.
Added `RoundBorderLineColorContext` and `RoundBorder` type
Added `RoundBorderLineContext`
Fixed doc in `RoundBorderLineColorContext`
Added `AddRoundBorder` trait
Arranged `pub use` alphabetically
Merge branch 'master' of https://github.com/bvssvni/rust-graphics

Conflicts:
	src/lib.rs