Lens phase function generation

[kaanaksit]

odak needs a lens phase function generation routine to generate phase patterns for various lenses (quadratic phase functions). Steps that are required to implement are as follows:

• Fork odak,
• In your own fork implement a phase function generation routine in odak.wave specifically in here.
• Add a test routine with a name test_lens_phase.py to test folder found in here. Other test routines such as this one can help in writing a test routine for this case.
• Commit all the changes to your fork.
• Once you are done at your fork, add a pull request to main repository of odak using this link.

Do not hesitate to ask any questions during your implementation.

[kaanaksit]

Mentioning @praneethc just for visibility.

[kaanaksit]

ae54c05 resolves this issue.