Categorize the examples for each section

[tom-tan]

This is a preparation to #37.

Currently all the examples are located in _include/cwl directly.
It is a little bit hard for contributors and users who want to learn CWL to find examples that are used in a section in user guide.

This request moves examples to the directory that corresponds to the file in _episodes, i.e. the section in user guide.
After merging this request, it makes easier to find the corresponding examples for each section.

Note: I removed createfile-job.yml and empty.json because they are not referred by any sections.

[tom-tan]

ping!

[mr-c]

Thank you @tom-tan ! I had accidently "un-watched" this repo and missed your PR.

[tom-tan]

Thanks!