Partially (or fully?) addresses#15

In this PR I only addedclojure-ts-extra-def-forms variable. I think we can add low-level customization if there is a request for that. For now dynamic font-lock from CIDER and this variable should cover most of the users needs.

Before submitting a PR mark the checkboxes for the items you've done (if you
think a checkbox does not apply, then leave it unchecked):

• The commits are consistent with ourcontribution guidelines.
• You've added tests (if possible) to cover your change(s). Bugfix, indentation, and font-lock tests are extremely important!
• You've runM-x checkdoc and fixed any warnings in the code you've written.
• You've updated the changelog (if adding/changing user-visible functionality).
• You've updated the readme (if adding/changing user-visible functionality).

Thanks!