Wrap sax in trycatch

Resolves #112 by wrapping calls to sax's write and end methods in a try/catch. If we catch an exception, we trigger the exception on the sax parser -- from where it would have originated had the parser been catching parse errors.

This is not complete. The error-handling is currently suboptimal, as it will trigger an error and then never end parsing without user intervention (see L#58 in the test). So, I'm considering making `this.push(null)` automatic.

@kof @alltom Any thoughts?
On this specific issue: `try/catch` prevents V8 from using Crankshaft, the optimizing compiler. Definitely worth the overhead. jsperf tests initial speed, you would need to loop to have a noticeable effect.

Regarding XML-parsers: I'm not sure feeds should be parsed using strict XML parsers, many authors don't care about namespaces. Anyway, I'll probably add rudimentary support for them (primarily for HTML) in a future version.

htmlparser2 ships (as a leftover from the original htmlparser project) with a rudimentary RSS/Atom parser, maybe this can be extended to be a fast alternative to this module (if you *really* care about speed).