Finished the Vector definition.

This complete what is needed for the definition of Vector2, Vector3, and Vector4.

This required a trigonometry section, fleshing out the rest of the Number, ToNumber,
and FromNumber section, correctly defining all the available function for the Real
trait, and defining several constants.

tests/lib.rs

@@ -1,3 +1,5 @@
 extern crate sigils;
 
+
+mod constants;
 mod vector;