Expanded parser for advanced input

[CodyJasonBennett]

This pull request expands on #31 by creating a new parseProps method that expands on parsing float values and introducing conversions with modifiers like deg(180) to specify 180 degrees or π radians.

You can play around with this in the updated tests.

I have not yet applied this to the internal applyProps method as I'm unsure of the exact implementation, as this is a recent development.

[hmans]

Thank you for the PR! Do you mind if I take this as a base and refine it further? I would like to do the following things:

• integrate it into applyProps, obviously ;-)
• refactor it so we can hook in additional transformations later (I'm not sure if there's ever going to be more of them, but I would prefer this to be a "transforms" feature, not a "degree to radians" one, if you catch my drift; just to be able to reason about the code better)
• do another pass of potential performance optimizations (eg. run strings through parseFloat as little as possible)

[CodyJasonBennett]

Sure thing.

[hmans]

Thanks, this will now continue in #33!