Minor IE fixes

for #3 and #4.  Some documentation on the current IE situation is needed on both this and Annotator to explain `rangy`, etc.
We don't, but it's good not to have magic numbers in general.

> On Sep 23, 2014, at 6:18 PM, Randall Leeds <notifications@github.com> wrote:
> 
> In src/range.coffee:
> 
> >          # Everyone else
> > -        (a, b) -> a.compareDocumentPosition(b) & 16
> > +        (a, b) -> a.compareDocumentPosition(b) &
> > +          Node.DOCUMENT_POSITION_CONTAINED_BY
> > +
> > +      else
> Do we even need this clause if we're using the shims?
> 
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