[Fix #111] Adding API for filtering object while indexing

[safwanrahman]

This fixes #111. We need to add documentation for this. But I am not sure where to add it.
overwriting the should_index_object and returning a boolean value should determine which object should be index.

For example, if we want to index Car only with Red color, we can write following

class Car(Document):
    def should_index_object(self, obj):
        if obj.color == "RED":
            return True
        else:
            return False

[safwanrahman]

@barseghyanartur @alexgarel Any thoughts about the code and where should we document it? any suggestion about the API or anything?

[barseghyanartur]

@safwanrahman:

What about in here: es_index? Seems quite logical to me.

[safwanrahman]

@barseghyanartur I was also thinking same. Lets see what @alexgarel thinks about this, as he is good at documentations.

[alexgarel]

What about in here: es_index? Seems quite logical to me.

I think this is a good idea ! It's not that at this point documentation is in a ideal state, but better put this information somewhere and move it latter, if needed.

Also put a docstring on should_index_object explaining the feature. (a lot of us look directly in the code + it would autodocument when we setup sphinx to do so)

[willbarton]

We've discovered the bug described in #111 and were looking at potential fixes and work-arounds. Is this PR just waiting on documentation?

[safwanrahman]

@willbarton Yes. it is waiting for the documentation. It will be great help if anyone can write something up!

[barseghyanartur]

@safwanrahman:

Shall I just do this? And it could be improved later on (if needed).

@safwanrahman:

What about in here: es_index? Seems quite logical to me.

[safwanrahman]

@barseghyanartur Sure! 🚀

[safwanrahman]

Seems like we need to merge this rathar than waiting for documentation! Added docstring though! 😅