add direction support to shear

[sizhky]

Tasks like OCR need shear in x direction only.
This pull request adds an ability to add shear only in x, or y or both directions while creating pipeline.shear

E.g.

p = Augmentor.DataPipeline(ims, labels)
p.shear(probability=1, max_shear_left=10, max_shear_right=10, direction=['x'])

[mdbloice]

Hi @sizhky, first of all, sorry for the late reply. Yes, this is a good idea. Let's add it but I would suggest we first make the user-facing option in Pipeline.py a little bit more friendly than directions=['x', 'y']. How about the direction can be either random, left, or right. Also, let's then change the parameter name to direction in this case. The signature would then be:

def __init__(self, probability, max_shear_left, max_shear_right, direction='random')

So it defaults to random, but you can specify left or right. We then need to change the code slightly in Operations.py to use these three possible parameters and adjust x and y accordingly there.