'**SUMMARY**
Calculates the grayscale value of R,G,B according to Luminosity Method
**PARAMETERS**
* *rgb* - a tuple of RGB values
**RETURNS**
Grayscale value according to the Luminosity Method
**EXAMPLE**
>>> c = Color.getLuminosity((22,35,230))
**NOTES**
Luminosity Method: value = 0.21*R + 0.71*G + 0.07*B'

@classmethod
def getLuminosity(self, rgb):

    return int((((0.21 * rgb[0]) + (0.71 * rgb[1])) + (0.07 * rgb[2])))
