Version 1.8.0

Add visual tests for the operators and the shapes.
Add shapes and operators to present visual tests:

• testElement(c="red", angle=0, size=1, center=false): Renders a test element. If no children is given, a cube with an arrow on top is rendered.
• testbedColor(alpha): Colorizes a test element.
• testbedExtrude(alpha): Extrudes and colorizes a test element.
• visualTest(index, length, width, title="test", margin=1, cols=0): Renders a test area, moving the tested shapes in it.
• visualTestSuite(length, width, title="test", margin=1, cols=0, center=false): Renders a test area for each child module, moving the tested shapes in it.

Fixes:

• properly use the build box and the render mode in the sample tube-cap
• typo in doc
• make the operation operator resilient to wrong parameters or children
• prevent dividing by 0 when count is 1 in rotate operator
• a wrong function was used to get the size of the chamfered box
• set the default height to 1 if none supplied to the link shape
• take care of the h parameter in buildVolume
• properly position the sample from the object to slice
• assume default values in rotateOrigin

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Pull requests:

• Feature/visual tests by @jsconan in #115
• Release 1.8.0 by @jsconan in #116
• Release 1.8.0 by @jsconan in #117

Full Changelog: v1.7.0...v1.8.0