Add config option for transcendental BASIC functions

Also move all transcendental functions to a separate source directory
Turn off these functions for all configurations for now

src/,,config_testing_38K.s

@@ -103,6 +103,11 @@
 ;; #CONFIG# BCD_SAFE_INTERRUPTS        YES
 
 
+; --- BASIC features
+
+;; #CONFIG# TRANSCENDENTAL_FUNCTIONS   NO
+
+
 ; --- Eye candy
 
 ;; #CONFIG# COLORS_BRAND               NO