Remove cruft
range: Improved test for an off-by-one error

The test removed by this commit was originally introduced in order to
demonstrate a failing case that the addition of [this line][1] fixed in
normalisation of serialized ranges.

[1]: https://github.com/openannotation/xpath-range/blob/b1827dd16b54d23e632c3da5fca4860c8d0dc080/src/range.coffee#L336

This commit replaces that test with a pair of tests that more clearly
demonstrate the intent and purpose of the test.

At the same time, it removes the Util.readRangeViaSelection function
that is only used in this test.
Merge pull request #8 from openannotation/off-by-one

Improved test for an off-by-one error
Remove unused #toRange method

This isn't used anywhere and is the only method in the repository which
makes direct use of W3C Range APIs on the document object. Removing this
coupling makes it easier to use this library with, for example,
Rangy[1].

[1]: https://github.com/timdown/rangy
Merge from upstream