Readme updates

[j042]

Overview

Updated readme and documentations to give a better overview of this project. I've also included some chores / clean ups here so that examples in readme works as it is. Changes are:

• more shortcuts. frequently used / main features are directly accessible at splinepy.*
• fitting clean up. tries to use less ifs. It seems that there's an issue with approximation
• microstructure tiles clean up. set some variables as class variable
• added TileLib - easy access to tiles

Checklists

• [ ] Documentations are up-to-date.
• [ ] Added example(s)
• [ ] Added test(s)

[j042]

Todo: background color, in modification plot nr.1 is wrong

[j042]

@jzwar @clemens-fricke are you happy with the background?

[j042]

todo: change extract bases' angle

[j042]

todo: add iges