parseUri() regex split up into smaller regexes

As a follow-up to #247, I figured that since I understand that giant regex in `parseUri`, I should break it up into smaller regexes, rather than one regex to rule them all.

The resulting regex is identical:
```
var protocol = /(?:(?![^:@]+:[^:@\/]*@)(http|https|ws|wss):\/\/)?/;
var user = /([^:@]*)/;
var password = /(?::([^:@]*))?/;
var userInfo = new RegExp('(?:(' + user.source + password.source + ')?@)?');
// e.g. www.google.com. The [a-f0-9] part is for ipv6
var host = /((?:[a-f0-9]{0,4}:){2,7}[a-f0-9]{0,4}|[^:\/?#]*)/;
var port = /(?::(\d*))?/;
var authority =
  new RegExp('(' + userInfo.source + host.source + port.source + ')');

var directory = /(\/(?:[^?#](?![^?#\/]*\.[^?#\/.]+(?:[?#]|$)))*\/?)?/;
var file = /([^?#\/]*)/;
var path = new RegExp('(' + directory.source + file.source + ')');
var query = /(?:\?([^#]*))?/;
var anchor = /(?:#(.*))?/;
var relative =
  new RegExp('(' + path.source + query.source + anchor.source + ')');

var re = new RegExp('^' + protocol.source + authority.source
                  + relative.source);

var oldRe = /^(?:(?![^:@]+:[^:@\/]*@)(http|https|ws|wss):\/\/)?((?:(([^:@]*)(?::([^:@]*))?)?@)?((?:[a-f0-9]{0,4}:){2,7}[a-f0-9]{0,4}|[^:\/?#]*)(?::(\d*))?)(((\/(?:[^?#](?![^?#\/]*\.[^?#\/.]+(?:[?#]|$)))*\/?)?([^?#\/]*))(?:\?([^#]*))?(?:#(.*))?)/;

undefined

re.source === oldRe.source

true
```