bugfix: convert ints to strings before write

Ensures all scalar values (like ints) are converted to string types before write.
Fix single item shorthand list parsing bug

This fixes a bug where shorthand lists made with `[` and `]` containing only
a single item would not be parsed correctly. The `_eat_items` utility function
did not take into account the fact that the list end character could be in the
first item. I've added a conditional to check for this case and not call
the `_eat_items` method, because the current behavior is expected for some
inputs that use `_eat_items`.
Update changelog
Merge pull request #830 from danielgtaylor/shorthand-list-fix

Fix single item shorthand list parsing bug. Fixes #830.
Update changelog with opsworks update
Add unittests for #829
Add changelog entry for #829
Merge branch 'tgolly-patch-1' into develop

* tgolly-patch-1:
  Add changelog entry for #829
  Add unittests for #829
  bugfix: convert ints to strings before write