Get rid of these ugly hacks now that Guzzle actually has an interface for the http client
add vendor/ to gitignore
changes to support Guzzle's new client interface
various improvements, see details

* added more param checking - low must be less then high
* changed checkQuota() from protected to public
* added userAgent getter/setter
* changed some magic numbers to constants (MIN_STRING, MAX_STRING)
added tests both with and without network access
added composer.lock to .gitignore