Simplify mousemove vs docmousemove handlers

Instead of the arcane `delete e.target`, mousemoves passes in an
optional target that docmousemove omits.

Also simplify and clarify comments.
Fix #312, seek ignoring mousemove target
Merge branch 'dev' into fix.seek-target
\slash not real LaTeX command, output as '/'

\slash isn't LaTeX, but '/' is: http://mathb.in/17532

Typing '/' results in LiveFraction, so need \slash so it's even possible
to type that character.

Also, not a delimiter so move out of the 'delimiters' section, to the
'various symbols' section.
\{open,close}curlybrace aren't LaTeX, use \{l,r}brace

http://mathb.in/17532

Keep \{open,close}curlybrace for backcompat
\caret and \underscore not real LaTeX commands

Can just use \_ for \underscore instead: http://mathb.in/17532

\caret is more annoying, settling for \text{^} (this is in
advancedSymbols.js anyway):
http://tex.stackexchange.com/questions/77646/how-to-typset-the-symbol-caret-circumflex-hat
Rename 'edited' hook to more accurate 'reflow'

Also under consideration was 'layout', but that has other meanings
whereas reflow is more specific:
https://github.com/mathquill/mathquill/pull/317#issuecomment-45383191

Just did:

    sed -i '' s/edited/reflow/g $(git grep -l edited)

and rewrote the README entry.

Recommend --word-diff-regex='\w+|\S' to view diff.
Rename API method 'redraw' more specific 'reflow'

The 'edited' hook was originally named 'redraw', and I mistakenly
renamed it in #241 thinking they should mean the same thing, but undid
that in the parent commit.

Just did:

    sed -i '' s/redraw/reflow/g $(git grep -l redraw)

and rewrote the README entry.

Recommend --word-diff-regex='\w+|\S' to view diff.
Merge pull request #323 from mathquill/fix.symbols

Fix symbols LaTeX output
Merge pull request #325 from mathquill/rename.edited-to-reflow

Rename 'edited' hook to more accurate 'reflow'
Simplify mousemove/docmousemove/selectTo

https://github.com/mathquill/mathquill/commit/deafecd34663057724b45849fc069030f3c25c2c#commitcomment-7541654
Merge pull request #321 from mathquill/feature.innerFields

Feature: .innerFields on static math instances
Merge pull request #322 from mathquill/fix.seek-target

Fix seek target
Merge branch 'dev' into api.options

Conflicts:
	src/commands/math.js
	src/commands/math/basicSymbols.js
	src/commands/text.js
	src/services/keystroke.js
	src/services/latex.js
These were all the same conflict: #325 changes all the instances of
'edited' to 'reflow', which are all adjacent to lines where
9d8fa6b1955779910b7af451ac962f57721e6513 added the options object as the
first argument to .finalizeTree(), .sibling{Created,Deleted}().

It's actually quite concerning how many places that is and how similar
the code is in all those places.