Add a define SSL_ALREADY_INITIALIZED

This define should be set if civetweb is embeded into a host application
that did already set up SSL (libcrypto).
See also comment "cryptolib_users = 1", issue #58

docs/Building.md

@@ -98,6 +98,7 @@ make build COPT="-DNDEBUG -DNO_CGI"
 | NO_SSL_DL                 | link against system libssl library   |
 | NO_FILES                  | do not serve files from a directory  |
 | SQLITE_DISABLE_LFS        | disables large files (Lua only)      |
+| SSL_ALREADY_INITIALIZED   | do not initialize libcrypto          |
 
 ## Cross Compiling
 

docs/Embedding.md

@@ -125,6 +125,10 @@ two threads: a master thread, that accepts new connections, and several
 worker threads, that process accepted connections. The number of worker threads
 is configurable via `num_threads` configuration option. That number puts a
 limit on number of simultaneous requests that can be handled by civetweb.
+If you embed civetweb into a program that uses SSL outside civetweb as well,
+you may need to initialize SSL before calling `mg_start()`, and set the pre-
+processor define SSL_ALREADY_INITIALIZED. This is not required if SSL is used
+only within civetweb.
 
 When master thread accepts new connection, a new accepted socket (described by
 `struct socket`) it placed into the accepted sockets queue,