Release the tutorial

[synw]

Hi. This lib looks good but it is not easy to start with. For people like me that are not great at maths and like to work with data in Dart it would be great to have a tutorial explaining the features with more details and examples.
This way I could figure out what some mysterious and interesting things I found in the api doc are for, like "Interpolates linearly between sourceA and sourceA with a factor t"