Collection: reformat doc-strings to follow PEP 257

This commit reformats the doc-strings in the 'collection.py' file. Also,
fixed some typos and misspellings. The doc-strings are now capitalized, and
the 'arguments' and 'keywords' are sandwiched between single quotations.

[1] https://peps.python.org/pep-0257/

Author: pedramardakani