* Support Unicode \ll and \lll
Fixes issue #1271
* Adjust \underset alignment and spacing
Fixes issue #1288.
1. Fixes vertical alignment by keeping the base element on the baseline.
2. Assigns horizontal spacing to \underset in a manner that aligns with LaTeX `\binrel`
* Fix flow error
* Add comment
* Allow for shift of mathops
* Update screenshots
* Test for nested ordgroups
* Set \stackrel spacing class to mrel
* Fix lint error
* Better determination of atom type
* Add comment.
* Add `suppressBaseShift` to ParseNodeTypes
* Support Unicode Big Operators
This is the sixth in a series of PRs to give KaTeX the ability to recognize Unicode character input.
This is the final PR in this series that will submit characters in bulk. After this, there come some characters whose alias or atom type was not obvious. I'll turn in PRs for them, too, but only after they are vetted.
* Move constants outside of main functions
* Replace ∫ with \u222b
* Add backslash
