* Rewrite spacing commands as macros
Fix#1130 by defining `\!`, `\negthinspace`, `\,`, `\thinspace`, `\:`,
`\medspace`, `\;`, `\thickspace`, `\negmedspace`, `\negthickspace`,
`\enspace`, `\enskip`, `\qquad`, `\quad` as macros.
Fix#1036 by defining a new `SpaceNode` in mathMLTree that recognizes
all special space amounts from
https://www.w3.org/TR/2000/WD-MathML2-20000328/chapter6.html
* Fix <mspace> rendering and add a test to catch it
* Update screenshots
* Wrap special space characters in <mtext>
* Update screenshots
* Fix MathML escaping behavior
* Fix flow typos
* Fix Unicode-chrome
* Reimplement mod operators in terms of macros
* Rerun ModScript
* Remove excess table entries (now already macros)
* Fix bmod