Rectified errors in document.txt and paginator.py

[kedar2a]

doc/document.txt:

• In the documentation, variable name user_collection is reused in subsequent code as the user_col.
• This confusion is cleared and error in the documentation is fixed.

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mongokit/ paginator:

• The comment explaining each Paginator property (at some places) was having same copy-paste/mistyping.
• So, the appropriate property explanation is added.