[Parsers] Adding a working, but slower SAX parser and not using EXPAT until node-expat is fixed

Until this https://github.com/node-xmpp/node-expat/issues/102#issuecomment-64171703 is fixed

*	new file:   lib/expat_parser.js
- Separating the parsers in the lib directory.
- This is still a broken version.

*	new file:   lib/sax_parser.js
- Adding the working version of SAX, but way slower.

*	modified:   package.json
- Adding the ltx library, that has the sax parser.

*	modified:   src/index.js
- Organizing the requires section with the parsers.
- Refactoring the loading vs parsing
- Just switch the implementation of the parser on
  the requires or on the code.

*	modified:   test/index.js
- Updating the test to load a different file. Verified
  that the EXPAT parser is still broken for different
  files.

*	new file:   test/pom2.xml
- A second file for testing just in case.