[rshapes] Review DrawGradient color parameter names

[Paperdomo101]

void DrawCircleGradient(int centerX, int centerY, float radius, Color color1, Color color2);
void DrawRectangleGradientV(int posX, int posY, int width, int height, Color color1, Color color2);
void DrawRectangleGradientH(int posX, int posY, int width, int height, Color color1, Color color2);
void DrawRectangleGradientEx(Rectangle rec, Color col1, Color col2, Color col3, Color col4);

Have been changed to:

void DrawCircleGradient(int centerX, int centerY, float radius, Color inner, Color outer);
void DrawRectangleGradientV(int posX, int posY, int width, int height, Color top, Color bottom);
void DrawRectangleGradientH(int posX, int posY, int width, int height, Color left, Color right);
void DrawRectangleGradientEx(Rectangle rec, Color topLeft, Color bottomLeft, Color topRight, Color bottomRight);

Additionally, in rshapes.h old NOTE: comments above aforementioned functions have been removed as color order is now self-explanatory.

[raysan5]

@Paperdomo101 thanks for the review!