Redesign of SDC algorithm

Issue/feature addressed

This is a redesign of the SDC algorithm.

Proposed solution

• The calculation integration matrix has been moved to Polylib.cpp.
• The SDC algorithm has been split into sub-functions to compute separately the initial guess and the SDC iteration loop.

Tests

Suggested reviewers

Please suggest any people who would be appropriate to review your code.

Notes

Please add any other information that could be useful for reviewers.

Checklist

• [ ] Functions and classes, or changes to them, are documented.
• [ ] User guide/documentation is updated.
• Changelog is updated.
• [ ] Suitable tests added for new functionality.
• Contributed code is correctly formatted. (See the contributing guidelines).
• [ ] License added to any new files.
• No extraneous files have been added (e.g. compiler output or test data files).