Add some convenience geometry methods

[yck011522]

What type of change is this?

• Bug fix in a backwards-compatible manner.
• New feature in a backwards-compatible manner.
• Breaking change: bug fix or new feature that involve incompatible API changes.
• Other (e.g. doc update, configuration, etc)

Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your code.

• I added a line to the CHANGELOG.md file in the Unreleased section under the most fitting heading (e.g. Added, Changed, Removed).
• I ran all tests on my computer and it's all green (i.e. invoke test).
• I ran lint on my computer and there are no errors (i.e. invoke lint).
• I added new functions/classes and made them available on a second-level import, e.g. compas.datastructures.Mesh.
• I have added tests that prove my fix is effective or that my feature works.
• I have added necessary documentation (if appropriate)

[yck011522]

PR can close #896

[tomvanmele]

test fail on ironpython due to a missing fixture it seems

[jf---]

Cool! @tomvanmele pointed a preference for reverse over flip, I think that's an important point.

[yck011522]

I'm slightly inclined to keep the terminology borrowed from Rhino / Grasshopper where

• Vector (and other non tangible things, such as list) are reversed
• Lines (and other tangible entity, such as curves, meshes and surfaces) are flipped.

[gonzalocasas]

lgtm

about the flip vs reverse, I don't have a strong opinion, whatever you guys think it's best