make vector2 rotation direction explicit, deprecate CW default (#182)

docs/docs/utilities/vector2.md

@@ -103,7 +103,11 @@ vec = vec.rotate90();   // much better
 
     Alias for `normalize()`. 
 
-??? func "`#!cpp Vector2 Vector2::rotate(double theta)`"
+??? func "`#!cpp Vector2 Vector2::rotateCW(double theta)`"
+
+    Rotate the vector by angle $\theta$ in the clockwise direction.
+
+??? func "`#!cpp Vector2 Vector2::rotateCCW(double theta)`"
 
     Rotate the vector by angle $\theta$ in the counter-clockwise direction.
 

include/geometrycentral/utilities/vector2.h

@@ -58,9 +58,11 @@ struct Vector2 {
 
   Vector2 normalize() const;
   Vector2 normalizeCutoff(double mag = 0.) const;
-  Vector2 unit() const; // alias for normalize
-  Vector2 rotate(double theta) const;
-  Vector2 rotate90() const;
+  Vector2 unit() const;                  // alias for normalize
+  Vector2 rotate(double theta) const;    // DEPRECATED, WARNING: rotates clockwise
+  Vector2 rotateCW(double theta) const;  // clockwise
+  Vector2 rotateCCW(double theta) const; // counter-clockwise
+  Vector2 rotate90() const;              // counter-clockwise
 
   // Complex functions
   Vector2 pow(double p) const;  // complex power

include/geometrycentral/utilities/vector2.ipp

@@ -91,11 +91,19 @@ inline Vector2 unit(const Vector2& v) { return normalize(v); }
 inline Vector2 normalizeCutoff(const Vector2& v, double mag) { return v.normalizeCutoff(mag); }
 
 inline Vector2 Vector2::rotate(double theta) const {
+  return rotateCW(theta);
+}
+
+inline Vector2 Vector2::rotateCW(double theta) const {
   double cosTh = std::cos(theta);
   double sinTh = std::sin(theta);
   return Vector2{cosTh * x + sinTh * y, -sinTh * x + cosTh * y};
 }
 
+inline Vector2 Vector2::rotateCCW(double theta) const {
+  return rotateCW(-theta);
+}
+
 inline Vector2 Vector2::rotate90() const { return Vector2{-y, x}; }
 
 inline Vector2 Vector2::pow(double p) const {