Release 0.1.11: Beta-1 + serious bug fix

This release fixes a serious bug in the number() function that
returned wrong results when converting strings into negative decimal
numbers (issue #160).

Other than that, what is new in this release compared to 0.1.10 is
what was added in the 0.1.11-beta:

When creating objects for output the key can now be computed with a
JSLT expression.

Three functions have been added:

zip-with-index
zip
index-of

And, finally, the JSLT implementation has been made fully thread-safe
by making the regular expression cache thread-safe.