Enabling Case Conversion Test

This is for issue sass/libsass#461

Signed-off-by: Hampton Catlin <hcatlin@a002867f-d9b0-47ee-bdc3-c07d990ae810>
new test for invert issue at sass/libsass#456
Enabled existing color tests.
Added a color test showing the conversion handling of colors and color variables.
Moved colors test back to todo, as it seems like it may fail at the parse stage.
Coerce color name string to a color in color-names test.
Update color_output test to include more variations, and match the formate preservation in sass 3.4.
Update color names to use 'gray' instead of 'grey'
Added more color output test cases to show libsass divergence.