Add angle conversion functions

Signed-off-by: Slendi <slendi@socopon.com>

tests/angles.cpp

@@ -0,0 +1,15 @@
+#include <gtest/gtest.h>
+
+#include <smath.hpp>
+
+TEST(AngleReturnRadians, DegInput) {
+  EXPECT_NEAR(smath::deg(180.0), std::numbers::pi, 1e-12);
+}
+
+TEST(AngleReturnRadians, RadInput) {
+  EXPECT_DOUBLE_EQ(smath::rad(std::numbers::pi), std::numbers::pi);
+}
+
+TEST(AngleReturnRadians, TurnsInput) {
+  EXPECT_NEAR(smath::turns(0.5), std::numbers::pi, 1e-12);
+}