Update examples to make use of new features / syntax

[blairj09]

There are several places where examples can be updated to reflect the latest release.

For example, the "hello world" example currently returns the following warning:

Warning message:
Plumber tag `#* @png` is deprecated.
Use `#* @serializer png` instead.

We should look through examples and make sure they reflect current syntax and best practices.

[meztez]

I'll take a look through it this morning, add whatever I see to Improve Docs PR