winbuild: Added Visual Studio 2005 (VC8) project files

Added a more thorough version of the VC8 project files that exist in
the "vs" folder with the intention to add support for other versions of
Visual Studio. These files support side-by-side compilation, 32-bit and
64-bit builds as well as support for some of the third-party libraries
curl uses.
http2: Compile with current nghttp2, which supports h2-11
winbuild: Updated the VC++ make instructions following commit 11025613b9

* Added information regarding the February 2003 Platform SDK for VC6
* Updated the introduction to be similar to the IDE projects README
Makefile.vc6: added warnless.c to fix build
sasl: Combined DIGEST-MD5 message decoding and generation
sasl: Added initial stub functions for SSPI DIGEST-MD support
sasl: Renamed SSPI module following short name clash
ntlm: Moved the identity generation into shared SSPI code
Makefile.vc6: Follow up fix to commit 45d3f00803
Makefile.vc6: Added curl_sasl_sspi.c
http_negotiate_sspi: Fixed compilation when USE_HTTP_NEGOTIATE not defined