Add initial complex-number support

- Library type instead of builtin
 - All C complex functions implemented

Partial WIP: Needs more tests for edge cases.

std/math/complex/sin.zig

@@ -0,0 +1,25 @@
+const std = @import("../../index.zig");
+const debug = std.debug;
+const math = std.math;
+const cmath = math.complex;
+const Complex = cmath.Complex;
+
+pub fn sin(z: var) Complex(@typeOf(z.re)) {
+    const T = @typeOf(z.re);
+    const p = Complex(T).new(-z.im, z.re);
+    const q = cmath.sinh(p);
+    return Complex(T).new(q.im, -q.re);
+}
+
+const epsilon = 0.0001;
+
+test "complex.csin" {
+    const a = Complex(f32).new(5, 3);
+    const c = sin(a);
+
+    const re = c.re;
+    const im = c.im;
+
+    debug.assert(math.approxEq(f32, re, -9.654126, epsilon));
+    debug.assert(math.approxEq(f32, im, 2.841692, epsilon));
+}