Added the basic trigonometric functions.

These were moved to their own trait and removed from the definition of
a Real number. This allows the definition of a trigonometric function
to call a different libc trig function depending on type.

examples/trig.rs

@@ -0,0 +1,47 @@
+extern crate pact;
+extern crate sigils;
+
+
+
+use ::sigils::{Constants, Degree, Radian, Trig};
+
+
+
+fn main()
+{
+   let mut val: f64;
+   let mut degrees: Degree<f64>;
+   let mut radians: Radian<f64>;
+
+   val = Constants::QUARTER_PI;
+   val *= 6f64;
+   radians = Radian::new(val);
+   degrees = Trig::acos(Trig::cos(radians));
+
+   println!("{:?}", radians);
+   println!("{:?}", degrees);
+   println!("");
+
+   radians = Radian::new(Constants::QUARTER_PI);
+   radians = Trig::acos(Trig::cos(radians));
+   degrees = Degree::from(radians);
+
+   println!("{:?}", radians);
+   println!("{:?}", degrees);
+   println!("");
+
+   degrees = Degree::new(270.0f64);
+   radians = Trig::acos(Trig::cos(degrees));
+
+   println!("{:?}", degrees);
+   println!("{:?}", radians);
+   println!("");
+
+   degrees = Degree::new(90.0f64);
+   degrees = Trig::acos(Trig::cos(degrees));
+   radians = Radian::from(degrees);
+
+   println!("{:?}", degrees);
+   println!("{:?}", radians);
+   println!("");
+}