MINOR: ssl: rename and document the tune.ssl.cachesize option

Its was initially called "tune.sslcachesize" but not documented, let's
rename it and document it.

doc/configuration.txt

@@ -475,6 +475,7 @@ The following keywords are supported in the "global" section :
    - tune.rcvbuf.server
    - tune.sndbuf.client
    - tune.sndbuf.server
+   - tune.ssl.cachesize
    - tune.zlib.memlevel
    - tune.zlib.windowsize
 
@@ -849,6 +850,16 @@ tune.sndbuf.server <number>
   to the kernel waiting for a large part of the buffer to be read before
   notifying haproxy again.
 
+tune.ssl.cachesize <number>
+  Sets the size of the global SSL session cache, in number of sessions. Each
+  entry uses approximately 600 bytes of memory. The default value may be forced
+  at build time, otherwise defaults to 20000. When the cache is full, the most
+  idle entries are purged and reassigned. Higher values reduce the occurrence
+  of such a purge, hence the number of CPU-intensive SSL handshakes by ensuring
+  that all users keep their session as long as possible. All entries are pre-
+  allocated upon startup and are shared between all processes if "nbproc" is
+  greater than 1.
+
 tune.zlib.memlevel <number>
   Sets the memLevel parameter in zlib initialization for each session. It
   defines how much memory should be allocated for the intenal compression

src/cfgparse.c

@@ -563,7 +563,7 @@ int cfg_parse_global(const char *file, int linenum, char **args, int kwm)
 		global.tune.chksize = atol(args[1]);
 	}
 #ifdef USE_OPENSSL
-	else if (!strcmp(args[0], "tune.sslcachesize")) {
+	else if (!strcmp(args[0], "tune.ssl.cachesize")) {
 		if (*(args[1]) == 0) {
 			Alert("parsing [%s:%d] : '%s' expects an integer argument.\n", file, linenum, args[0]);
 			err_code |= ERR_ALERT | ERR_FATAL;