Updates README per 936dc29d9b3a1d7432089962ecdbbaefd36f0d8b

• 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.