IE fix: always append preview element to body

text was blank in contenteditables in IE
repalce $ with jQuery

for maximum compatibility with pernickety pages!
add MIT licence

fixes #1
find tag containing anchor node before looking for maths

pasting text into a contenteditable can create multiple adjacent text nodes. We need to find the parent tag node containing the selected text node so that we get all the text.
cope with adjacent text nodes

Scanning for maths used to fail when it was spread across two text nodes adjacent to each other.
Now we find the parent tag node, so we get all of the text.
preview follows scroll

The preview moves to the correct position when the text area is scrolled.
fix detection of ignored tags
add position option

options.position and options.previewPosition can position the preview relative to the container.
They follow the jquery UI $.position syntax, i.e. '<left|center|right> <top|center|bottom>'.
update jquery; use jquery.migrate
Merge branch 'master' into gh-pages

Conflicts:
	index.html
	writemaths.js
fix something?

not sure what was going wrong