'**SUMMARY**
Calculates the grayscale value of R,G,B according to Lightness Method
**PARAMETERS**
* *rgb* - a tuple of RGB values
**RETURNS**
Grayscale value according to the Lightness Method
**EXAMPLE**
>>> c = Color.getLightness((22,35,230))
**NOTES**
Lightness Method: value = (max(R,G,B)+min(R,G,B))/2'

@classmethod
def getLightness(self, rgb):

    return int(((max(rgb) + min(rgb)) / 2))
