Perform manual string parsing for hasClass

This is faster and avoids additional memory pressure from temporary array objects.

Test: attributes - Has class (file: jquery.html)	cheerio x 46,072 ops/sec ±15.20% (61 runs sampled)	old x 4,477 ops/sec ±19.32% (46 runs sampled)
	jsdom x 3,123 ops/sec ±2.84% (89 runs sampled)
	Fastest: cheerio
Merge pull request #453 from kpdecker/hasclass-opt

Perform manual string parsing for hasClass