HTTP error codes are renamed and no longer a typedef'd enum
Moved response key constant to FAURLResponseValidator
Renamed HTTP validators to better match what they are validating
Made responseValidator on FAURLConnection strong so that validator objects do not have to be kept track of elsewhere
Added error domain and code for when a download stream reaches its capacity before it has finished writing
Improved FAURLConnectionDownloadTask stream handling by checking for hasSpaceAvailable and clearing out bytes from the buffer that have been successfully written to the stream