replace textfilter functions with one-fits-all version

* replaces filtertext() with a version with a dozen of single filters
  that can be used in any combination
* defines classes of allowed characters for strings for various uses
  (see protocol.h line 153ff)
* now the allowed charset of, for example, player names is defined
  in one location only
* fixes issue #58

source/src/log.cpp

@@ -81,7 +81,7 @@ bool logline(int level, const char *msg, ...)
     if(!enabled) return false;
     if(level < 0 || level >= ACLOG_NUM) return false;
     defvformatstring(sf, msg, msg);
-    filtertext(sf, sf, 2);
+    filtertext(sf, sf, FTXT__LOG);
     const char *ts = timestamp ? timestring(true, "%b %d %H:%M:%S ") : "", *ld = levelprefix[level];
     char *p, *l = sf;
     do