Support intersect of mixed interval types

[kevmal]

Closes #324, Closes #323

• Fix isIntersection bug
• Add support for intersect of mixed interval types (intersect of LeftOpen with RightOpen for example)

Description

Adds support for intersect on mixed interval types. Added tests for isIntersect as well as intersect. Ran FsCheck against both functions, could include those tests too if needed/wanted.

[Required] please make sure you checked that

• [x] The project builds without problems on your machine

[Optional]

• [x] Added unit tests regarding the added features