added parse_number

docs/lib-parse_number.md

@@ -0,0 +1,12 @@
+# parse_number
+
+Parses the string argument as an number. It depends on the `split_str` and the `sub_str` functions so remember to include split_str.scad and sub_str.scad.
+
+## Parameters
+
+- `t` : A String containing the number representation to be parsed.
+
+## Examples
+
+	echo(parse_number("10") + 1);    // ECHO: 11
+	echo(parse_number("-1.1") + 1);  // ECHO: -0.1