Amend comments: do not be confused about generators and iterators

Amend comments: do not be confused about generators and iterators

Iterators and generators are not the same things. Generators is a more narrow
concept. Generators are functions which yield elements.

Fix up commentaries where I mixed these terms. Call all my functions with
'yield' - generators. Also, prefer saying 'generator yields' to 'generators
generates' just to be more clear about what I am trying to say.

Fix a couple misspelled words and confusing sentences while on it.

No functional changes.

Change-Id: Ia87b1a6441c293aab2ad45e2cb762f388b49ea35
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@intel.com>