Update from deprecated 'colorToRGBA' to new name 'colorToSRGBA'.

See diagrams-lib@bfc8be9.
minor documentation fix, need extra False parameter in renderDia example
add renderCairo function for more convenient use of the cairo backend
big improvements to cairo documentation
add default case of PNG in renderCairo
bug fix: takeExtension actually leaves . as part of the output
Enable Travis IRC notifications
bump version to 0.6.1
whitespace/import/pragma cleanup
add Show instance for Options Cairo R2
travis: don't use monoid-extras and dual-tree from git anymore
Updates for new trail API.
Merge pull request #31 from diagrams/bee-coh

Updates for new trail API.