Update documentation
Indent
Ignore /test.rb
Indent
Add Color.==, extend unit tests
Add Collection
Use Collection in Chart and update example file
Add Border
Format
Allow creating a color from a string
Add format to axis
Allow creating a color from a single number; raise exceptions when a value is out of range
Add Border.color
Tics mirroring
Do plot border in example
Legend
Use pdfcairo terminal instead of pdf