Added Degree (Angle)
Add test about velocity

Signed-off-by: Clement Escoffier <clement.escoffier@gmail.com>
Fix velocity definition

Signed-off-by: Clement Escoffier <clement.escoffier@gmail.com>
Implement hashCode

Signed-off-by: Clement Escoffier <clement.escoffier@gmail.com>
Implement equals

Signed-off-by: Clement Escoffier <clement.escoffier@gmail.com>
Fix bug in map manipulation when removing a SystemOfUnits

Signed-off-by: Clement Escoffier <clement.escoffier@gmail.com>