ENH: Add 2D versions of several baseline algorithms

[derb12]

Description

Added two dimensional versions of several baseline correction algorithms, with the main focus being on polynomials, Whittaker smoothing, and penalized splines. Documentation for the added 2D algorithms is complete. The only remaining todo is to add a 2D optimizer that applies a selected 1D baseline correction method along each individual row and/or column, and maybe an example or two in the documentation.

Type of Pull Request

• [ ] Bug Fix
• [x] New Feature
• [ ] Miscellaneous Changes (refactor, code improvements, etc.)
• [x] Documentation or Example Programs

Pull Request Checklist

• [x] New code and/or documentation is valid for use with the BSD 3-clause license.
• [x] New code is fully documented with docstrings that follow Numpy style, if applicable.
• [x] New code follows PEP 8 standards as closely as possible, if applicable.
• [x] Added/updated tests and ensured they pass locally, if applicable.
• [x] Verified that documentation builds locally, if applicable.

[derb12]

The one test failure is from pentapy v1.0 being unable to be installed from source (numpy not found?). Weird issue since I can't replicate locally on ubuntu or windows, but I may have to just bump the required version to one with an available wheel for python 3.8. Does not block merging this branch.