While running 'make' command, Sphinx throws following warning messages:
```
pym/docs/modules.rst:218: WARNING: Inline interpreted text or phrase
reference start-string without end-string.
pym/docs/modules.rst:219: WARNING: Inline interpreted text or phrase
reference start-string without end-string.
```

This happens because there is a space present before closing caret (`)
character.

This commit contains following changes:
  - Fix spell of following words:
      - below (bellow -> below).
      - interpreter (interpeter -> interpreter).
  - Replace "and" word with "a".
  - Fix formatting issue in "Module os" section.
  - Add missing "by" word in "Request module" section.

This commit contains following changes:
  - End complete sentence with a period punctuation.
  - End sentence with colon punctuation, if next sentence contains
    explanation of it.

Separate "important" section.