Move \int down among misc. symbols

Instead of at the top of symbols.js
Reorder LatexCmds/CharCmds registration for \prime #cosmetic
Fix LaTeX parsing of '

http://mathb.in/16257

It just being on CharCmds was a total mistake, it's a real LaTeX
command, we output &prime; as ', obviously we should parse ' as &prime;.

Technically in LaTeX it's a macro for ^\prime, so we shouldn't parse
\prime as being the same, but &prime; looks more like ^\prime (slash '),
so for now, just parse \prime wrong.
Move non-backslash-instantiated commands to top

...of symbols.js

(i.e. commands that can be typed without LatexCommandInput)
Add dollar sign symbol \$

Adds support for parsing \$; also makes it so that without
CharCmds.$ = TextBlock, typing $ will default to typing the
dollar sign symbol, \$.
Move VanillaSymbol and BinaryOperator to math.js

...next to Symbol, from symbols.js, because about to split up basic and
advanced symbols, but both depend on VanillaSymbol and BinaryOperator.
Split up symbols.js into {basic,advanced}Symbols.js
Separate out LatexCommandInput from commands.js

The rest of commands.js comes up in basic mathematics.
Ensure MathQuill.TextField's are .mathquill-textbox

https://github.com/mathquill/mathquill/commit/f4ce7e9647cb2d3d05ff47e0551a7ed7ee258057#commitcomment-6262646
Match wording of README and publicapi.js comments #docs

In particular, consistently say "HTML element" everywhere, instead of
sometimes also saying "DOM element".

Also, I originally wrote multiple variants of the global MathQuill() fn
comment, meaning to delete all but one, but left 2, so combine them.
And copy over explanation that identity of API object is guaranteed.
Fix MathQuill::revert(), test with README example
Fix and test passing null/undefined to global API fns

Include tests for every README example
Don't use .mathquill-embedded-latex for styling

Was being used to style inner math fields (\MathQuillMathField{}), but
want .mathquill-embedded-latex to be entirely external. Now its only
mention internally is on document ready, find all
.mathquill-embedded-latex and render them as MathQuill.StaticMath().

Styling should be done with only internal CSS classes like
.mathquill-rendered-math (which really should be .mq- not .mathquill-).
Rename .mathquill-{embedded-latex => static-math}

Matching the name MathQuill.StaticMath().

This one's easy because it was already basically only used externally.

Recommend --word-diff-regex='[a-z-]+|.' to view diff.
Rename external .mathquill-{editable => math-field}

Styling should be only done with internal CSS classes, so now the README
refers to .mathquill-math-field and never .mathquill-editable (which
should be .mq- not .mathquill-).

The new .mathquill-math-field CSS class is entirely external, its only
mention internally is on document ready, find them all and render them
as MathQuill.MathField().

Recommend --word-diff-regex='[a-z-]+|.' to view diff.
Rename external .mathquill-{textbox => text-field}

Styling should be only done with internal CSS classes, so now the README
refers to .mathquill-text-field and never .mathquill-textbox (which
should be .mq- not .mathquill-).

The new .mathquill-text-field CSS class is entirely external, its only
mention internally is on document ready, find them all and render them
as MathQuill.TextField().

Recommend --word-diff-regex='[a-z-]+|.' to view diff.
Rename .mathquill-editable to .mq-editable-field

It's an internal CSS class used for styling, and this matches the name
EditableField.

Recommend --word-diff-regex='[a-z-]+|.' to view diff.
Unify .mathquill-textbox and .mq-text as .mq-text-mode

.mq-text is just straight up replaced with .mq-text-mode (named after
TeX's text mode, as opposed to math mode).

.mathquill-textbox is replaced with .mq-editable-field.mq-text-mode
("an editable field in text mode"), so once .mathquill-rendered-math
becomes .mq-math-mode, TextField's will be symmetrical with MathField's,
which will be .mq-editable-field.mq-math-mode.

We don't have to worry about selectors for TextBlock's (.mq-text) now
accidentally selecting TextField containers, because those selectors
are always nested inside .mathquill-rendered-math's.

Recommend --word-diff-regex='[a-z-]+|.' to view diff.
Rename .mathquill-rendered-math to .mq-math-mode

Named after TeX's math mode, symmetrical with .mq-text-mode.

Nicely enough, makes the TextField constructor even more symmetrical
with the MathField constructor.

Recommend --word-diff-regex='[a-z-]+|.' to view diff.
Rename .{mathquill => mq}-root-block

For consistency with all of MathQuill's other CSS classes