convert B. Fixed-point math & LUTs to markdown (#82)

* automatic conversion of B. Fixed-Point Numbers

* manual cleanup of B. Fixed-Point Numbers and LUTs

- add to SUMMARY.md
- replace table of contents with <!-- toc -->
- distinguish $10.78 near the beginning from hexadecimal
- specify "nowadays" relative to when FPUs became standard in PCs
- set language for 9 code blocks
- restore HTML for 1 figure and 4 tables and autonumber them
- convert 10 equations to MathML via LaTeX and autonumber them
- capitalize LUTs
- replace ^n^ with <sup>n</sup> and ~a~ with <sub>a</sub>

* B. fixed: fix a handful of markup problems

- convert two missed backslash divisions to use floor symbol
- fix markup error in caption of fig:lerp (fig B.1)
- use Wayback Machine to fix link to cited article
  "An Introduction to Fixed Point Math" by Brian Hook

---------

Co-authored-by: Antonio Vivace <avivace4@gmail.com>

content/SUMMARY.md

@@ -39,7 +39,7 @@
 ---
 
 [Appendix A - Numbers, bits and bit operations](./numbers.md)
-[Appendix B - Fixed-point math & LUTs]()
+[Appendix B - Fixed-point math & LUTs](./fixed.md)
 [Appendix C - Vector and matrix math]()
 [Appendix D - More on makefiles and compiler options](./makefile.md)
 [Appendix E - Make via editors]()