implemented split operation in RhinoBrep

[chenkasirer]

Added split operation to RhinoBrep.
Added GH example to Brep tutorial.

• New feature in a backwards-compatible manner.

Checklist

• 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 have added necessary documentation (if appropriate)

[gonzalocasas]

LGTM!