Added support for IP-literal in the Host header and request line (ticket #1).

Added support for IP-literal in the Host header and request line (ticket #1).

Additional parsing logic added to correctly handle RFC 3986 compliant IPv6 and
IPvFuture characters enclosed in square brackets.

The host validation was completely rewritten. The behavior for non IP literals
was changed in a more proper and safer way:

 - Host part is now delimited either by the first colon or by the end of string
   if there's no colon. Previously the last colon was used as delimiter which
   allowed substitution of a port number in the $host variable.
   (e.g. Host: 127.0.0.1:9000:80)

 - Fixed stripping of the ending dot in the Host header when the host was also
   followed by a port number.
   (e.g. Host: nginx.com.:80)

 - Fixed upper case characters detection. Previously it was broken which led to
   wasting memory and CPU.