websocket update

- added API documentation to libmicrohttpd.texi
- added websocket tutorial chapter to libmicrohttpd-tutorial and an much easier example for the tutorial
- added additional helper functions to ease the HTTP websocket handshake
- the code can now be compiled on Linux without errors
- changed sha1.c and sha1.h to the files provided by Evgeny (I replaced those files in src/microhttpd_ws/ with the files from src/microhttpd/ - maybe there is a smarter way...?)
- removed dependency for "htons" and "htonl" (these functions are now implemented in MHD_websocket.c; no need for OS-dependent files anymore)
- added an additional test script for testing of the library with any webbrowser (for manual practice test)
- several bugfixes
- parameters renamed
- special things clarified (fragmentation, RNG for client mode)

The new version of the API is at some points incompatible with the old version, but since it was in an experimental phase and it didn't compile on Linux, I guess this shouldn't bother anyone.
From my point of view, I am now finished with the library and it could go out of experimental.

doc/libmicrohttpd-tutorial.texi

@@ -68,6 +68,7 @@ Free Documentation License".
 * Improved processing of POST data::
 * Session management::
 * Adding a layer of security::
+* Websockets::
 * Bibliography::
 * License text::
 * Example programs::
@@ -109,6 +110,10 @@ Free Documentation License".
 @chapter Adding a layer of security
 @include chapters/tlsauthentication.inc
 
+@node Websockets
+@chapter Websockets
+@include chapters/websocket.inc
+
 @node Bibliography
 @appendix Bibliography
 @include chapters/bibliography.inc
@@ -128,6 +133,7 @@ Free Documentation License".
 * largepost.c::
 * sessions.c::
 * tlsauthentication.c::
+* websocket.c::
 @end menu
 
 @node hellobrowser.c
@@ -178,4 +184,10 @@ Free Documentation License".
 @verbatiminclude examples/tlsauthentication.c
 @end smalldisplay
 
+@node websocket.c
+@section websocket.c
+@smalldisplay
+@verbatiminclude examples/websocket.c
+@end smalldisplay
+
 @bye