Includes modules for rounded squares and triangles

This is clever in principle but poor in practice, because you have to assume the intention behind the centering command. Do you want to center based on the size (bounding box), or do you want to center based on the rotation if the triangle is equilateral? Easier to always assume bounding box centering and get rid of the trig.

Previously this was split between a hard "0.1" for the etch style module and a separate "0.1" for the spool etching. This unifies both as a single value.

Uses the enclosure_etch_style() helper function to simplify placement. Also removes the 3D difference() function to simplify rendering.

Using a triangle for the motor/left side and a circle for the idler/right side. The triangle requires less etching area than the square and should provide more contrast with the circle at smaller sizes / lower etching resolutions.

This should use the pre-calculated "enclosure_indicator_position_y" value along with all of the other etched indicators.

Visually, the symmetry looks better.

Although this looks better it's significantly more expensive to produce: the single-ended etched indicators add about $0.56 to the cost per enclosure @ Ponoko. The dual-ended etched indicators add $4.51, presumably because of the travel time between aligned indicators in the rasterized version.

This reverts commit 9e60870.