Added an isExternal method that's used to determine if a URL is external
Exclusion of external URLs happening in .queue method now (instead of when crawling links)
If a redirect occurs, it's never processed at that time - it instead queues the correct URL
Changed queue's "crawlLinksOnPage" to "isExternal" and updated logic:
 - will return false and stop processing any external URL when crawler's _crawlExternal property is false
 - will set page's isExternal property based on the isExternal argument
 - will set crawler._pages[key]'s crawlLinks property to the opposite of isExternal (undefined is true)
Rearranged tests into "unit" and "func" folders