Fix `equals` method not allowing override

[EdgarACarneiro]

The current implementation does not allow the overriding of the FlatInterval.equals method since internally some FlatInterval objects are created to optimise data handling. As such, if one does override the equals method with the new properties, the search method brakes.

Possible solutions:

• Stop creating FlatInterval objects inside the I2BplusTree and just use/ move around the valid times;
• Create a new method (e.g. intervalEquals) that just makes the comparison of the intervals. Then, this method is used for comparison with the FlatInterval objects inside the tree, while the equals method is used for comparison between objects introduced by the user.

[Nikovic]

Hello. Is this bug/missing feature still around? I'm a little confused because overwriting equals is currently shown in the usage notes of the readme. If the bug is still around, a note in the readme might be a good idea.

I will be using I2Bplus-tree for a programming project in the context of my bachelor's thesis, and I'm open to contributing. Introducing the intervalEquals method seems like a good + fairly easy fix.

[EdgarACarneiro]

Hey @Nikovic thanks for your question - I need to take a deeper look into it since it has been a while
I'll get back to you once I do so