Slic3r: 1.3.1-dev-54a31ee
OS: Ubuntu 18.04.4

Load STL
Select model.
Right click - Rotate - Around z axis...
Input 90 - press ok
Model moves 90 degrees counter clock wise as expected.
Input 90 - press ok
BUG Model doesn't move.
Input 0 - press ok
Model doesn't move. (As expected for relative rotations, but not absolute.)
Input -90 - press ok
BUG Model rotates 180 degrees.

Around x

Theres been a LOT of new features the last couple weeks, but so much of it is missing "intuitive" or "detail" from them:

Examples:

1. Right Clicks - sure we can come up with something better? Not intuitive
   

~~2) Typing, wait for result, type again... hmmm, I wonder, sliders

Automated tests are very helpful in maintaining a code base. All of BCAM's geometry calculations are well-suited for testing; I/O and GUI code is a little more difficult to test, but still very possible.

@snegovick, I'll start working on this, but I want your input before I get started. I'd like to write the tests using pytest, but that would add another external dependenc

Create version tags and create a stable C API interface that follows semantic versioning (https://semver.org/). A C API will make it easy to create bindings from other languages and allow for changes and updates to the underlying C++ implementation without breaking users.

A potentially small overhead will be incurred in copying from the C API structures/arrays to the C++ structures but should b