Modified Parametric Bed Bracket (tolerance adjustable)

This is another slight tweak of these parametric bed brackets.

Changes:
* Added a print tolerance parameter to adjust how tight the screw and spring holes will fit, defaulting to 0.1mm.
* Fixed the customizer logic for the parameter that specifies the screw size.
* Add customizer parameter for smoothness of curves.
* Big clean-up of the code to make it easier to read/modify.

For my upload I'm including versions that match all bed bracket sizes included in the original HyperCube Evolution download.

Please note that if the bed offset is too small there won't be enough room for the included adjustment thumbwheel. For those you should be able to use jdobry's bed leveling nut knob (https://www.thingiverse.com/thing:2853903/).

To use the OpenSCAD you'll need to also download b33j0r's metric OpenSCAD module from GitHub: https://github.com/b33j0r/Metric.