Add three operations for random changing image brightness color and contrast

[CarkusL]

Hi, I add three operations for random changing image brightness color and contrast.
It can be used like the following code.

`
import Augmentor
p = Augmentor.Pipeline("/path/to/images")
p.random_color(probablility=1,min_factor=0.5,max_factor=1.5)
p.random_contrast(probablility=1,min_factor=0.5,max_factor=1.5)
p.random_brightness(probablility=1,min_factor=0.5,max_factor=1.5)

`

[mdbloice]

Hi @deanzhanggit, looks good, thanks a lot for the efforts: one thing I did notice that would need to be fixed before I could merge it is where you randomise stuff (I'll add a few comments in your code). Any randomised assignment performed in the Operation sub-classes needs to be done outside of the do(image) function. Basically it should be done within perform_operation(image) but outside of do(image).
This is essential for the proper functioning of the ground truth related features.
M.

[mdbloice]

The line above would need to be moved to outside of the scope of do() to somewhere within perform_operation().

[CarkusL]

@mdbloice Thank you for pointing out my mistake. I have moved the
factor = np.random.uniform(self.min_factor, self.max_factor)
out of function do()

[mdbloice]

Same goes for this. It would have to be outside of do(), again because we may pass multiple images through here in the case of any ground truth augmentation and we need for them to have the same parameters applied to them all.