Merge branch 'release-1.3.20' into develop

* release-1.3.20:
  Bumping version to 1.3.20
  Update changelog with latest changes
  Add customizations for cloudsearchdomain command
Don't validate --endpoint-url for help subcommand

"aws cloudsearchdomain" has --endpoint-url validation because
it's a required option for that service.  However, we should
*not* be validating this when a user is just trying to get
help.

The fix is to move the validation to the operation-args-parsed.*
event, which is after all the help processing code.

I've also added integration tests that actually run the help command
for cloudsearchdomain to verify this behavior works.
Merge branch 'fix-csdomain-help' into develop

* fix-csdomain-help:
  Don't validate --endpoint-url for help subcommand
Update changelog with issue 828
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
Bumping version to 1.3.21
Merge branch 'release-1.3.21'

* release-1.3.21:
  Bumping version to 1.3.21
  Add changelog entry for #829
  Add unittests for #829
  Update changelog with opsworks update
  Update changelog
  Fix single item shorthand list parsing bug
  bugfix: convert ints to strings before write
  Update changelog with issue 828
  Don't validate --endpoint-url for help subcommand