Improvements to %g pull request

This code %g is preliminary.

Fixed some code style issues to match the current code style.

Added regression tests and help file updates to printf and strprintf.

Fixed use of magic number -4: using -P instead.

Noted two problem areas with XXX comments in qio.c:

    1) need a qprintfg function
    2) re-write to not modify conf->outdigits

help/strprintf

@@ -27,6 +27,13 @@ EXAMPLE
 	    "1.732051,	1.732051,1.732051  ,   ~1.7320,~1.7320,~1.
     "
 
+    ; c = config("display", 50);
+    ; fmt2 = "%g %g\n%g %g\n"
+    ; strprintf(fmt2, 1e5, 1e49, 1e50, 1e500);
+	    "100000 100000000000000000000000000000000000000000000000000
+    1e50 1e500
+    "
+
 LIMITS
     The number of arguments of strprintf() is not to exceed 1024.
 
@@ -39,7 +46,7 @@ SEE ALSO
 
     printf, fprintf, print
 
-## Copyright (C) 1999-2006  Landon Curt Noll
+## Copyright (C) 1999-2006,2018  Landon Curt Noll
 ##
 ## Calc is open software; you can redistribute it and/or modify it under
 ## the terms of the version 2.1 of the GNU Lesser General Public License