Properly handle unicode in XML extractor

Allow attribute and element names to be unicode.
Add comprehensive XML extractor test for UTF-8

Verify that text, elements names, attribute names, and attribute
values can all contain UTF-8 encoded characters.
Add JSON UTF-8 test

* Make sure that JSON extractor does not mangle UTF-8 encoding.

* Create common .hrl file to share macros.
Add UTF8 plain-text extractor test
Merge pull request #138 from basho/rz-utf8-tests

Extractor UTF8 tests (plus fixes to XML extractor)