* Removes references to the ruby script and holding space.
* Mentions the `file_concat` dependency.
* Removes the `ensure_newline`, `force`, and `ensure` parameter
definitions.
* Renames the `warn` parameter to `warn_header`.
* Removes all deprecation listings.
* Adds a list of removed features.
* Cleans up some stray line breaks.

Implements edits from @jbondpdx

* Updates table of contents
* Clarifies requirement
* Specifies the module version where functionality was removed.
* Clarifies changes to the `warn` parameter
* Additional tweaks for clarity

Final copy tweak

* Further clarify the nature of boolean values in `warn_header`.