proper array index validation (dash, unsigned int)

According to the spec
http://tools.ietf.org/html/draft-ietf-appsawg-json-pointer-06

   o  If the currently referenced value is a JSON array, the reference
      token MUST contain either:

      *  characters that represent an unsigned base-10 integer value
         (possibly with leading zeros), making the new referenced value
         the array element with the zero-based index identified by the
         token, or

      *  exactly the single character "-", making the new referenced
         value the (non-existant) member after the last array element.
remove JsonPointer.set() to avoid duplicate code w/ python-json-patch

json-patch (https://github.com/stefankoegl/python-json-patch/) should be used
for modifying JSON documents
fix running tests during travis build
fix validation of array indices
fix installing when not in source directory, fixes #3
bump version to 0.6
no leading zeros for array indices, as of draft 08
unambiguous array indices make pointers comparable
bump version to 0.7
mention RFC 6901
bump version to 1.0
ignore *.swp and files generated during packaging
add some documentation
README: add link to docs
let sphinx extract version, author from source
fix unicode literal quirks in Python 3.2
also target Python 3.3 and PyPy
Drop support for Python 2.5
mention supported Python versions in docs
add doctests for pairwise(iter)