Add polar plot

Add polar plot options.

Extras:
- Scatter plot function
- Code style fixes
- Set axis background color
- Tutorial

Todo:
- [x] Improve moving the y axis
    - [x] Also move the tick marks
    - [x] More flexibel do not use cm units..
    - ~~Work properly when x limits are set~~
- [x] Move x-ticks outside the axis, they are inside despite `tick align=outside`
- [x] Add degree (°) sign to x axis labels
- [x] Make degree sign optional, especially for y (radius) axis ticks
- [x] Histogram support
- [x] Allow radians as data values for x axis
     - [x] Make axis tick labels range (-π, .., 0, ..., π) (replace 180° by ±π)
- [x] Fix error when having multiple polarplot in a document (due to \newlength)
- [x] Fix y-axis label shift, it sometimes shifts to far..?
- [x] Add feature to allow manual setting of `axislabels`