csspp 1.0.6 published

I got the @return implemented. This means external functions can be used as expected.

I also wrote tests to verify all the external functions. There were a few bugs (wrong variable spelling and actual code that would not work.)

As I was working on that, I came the conclusion that we needed to have a percentage() function which is an internal function. We cannot use decimal_number() to create a percentage since we want to use that function to transform a percentage to a plain decimal number!

I also noticed that a lone dash (minus since in a place where we expect an expression) would crash the library code. This is fixed.