Correct http header parser

Case Insensitive:
http://stackoverflow.com/questions/5258977/are-http-headers-case-sensitive
http://stackoverflow.com/questions/9102931/can-lua-support-case-insensitive-method-calls

Characters: 
stackoverflow.com/questions/19028068/illegal-characters-in-http-headers
http://www.w3.org/Protocols/rfc2616/rfc2616-sec2.html#sec2.2
http://www.w3.org/Protocols/rfc2616/rfc2616-sec4.html#sec4.2
