update doc

docs/lib2-split_str.md

@@ -0,0 +1,16 @@
+# split_str
+
+Splits the given string around matches of the given delimiting character. 
+
+## Parameters
+
+- `t` : The source string.
+- `delimiter` : The delimiting character.
+
+## Examples
+    
+	include <util/sub_str.scad>;
+	include <util/split_str.scad>;
+	
+	echo(split_str("hello,world", ","));  // ECHO: ["hello", "world"]
+