WP2020 - NLP cleanup

[drowe67]

Clean up nlp.c clean up and add unit tests (ctests) to support

• remove todos
• review comments
• remove profiling marcos (I don't think they are used any more)
• remove 8-16 kHz resampling functions and 16 kHz support (we can discuss but I don't think it's needed any more)
• come up with some unit tests, e.g. to support ports to other platforms. Consider tests that have a statistical pass criteria, a floating point error may cause non-exact output on different machines. For example we could count gross errors over a sample file against had estimates, and/or use contrived signals such as codec2-dev/estn0
• unit test for pitch refinement. Make sure it really is refining. These days we probably have enough CPU for the full MBE cost function method. Optional - determine if we still need refinement.
• align variable names with codec.pdf
• bring plnlp.m back from codec2-dev, edit it, add instructions for it's use