Implement a basic form of redaction

Currently it only supports redaction of new files.

Redacting new parts of old files is still in the works, but seemed more
complicated so I did the new file version first.
Make SECRETS_SUFFIX not have a leading dot
Make add use check-hermit-profile script
Extract a function for creating hermit relative paths
Add functions to simplify the reuse of moving and linking code
Document the redact option for add
Stub out logic of how to mark redactions
Add a function for copying verbosely
Make all functions in add use local variables
Add a function to add files to a .gitignore in the current hermit profile
Implement redaction as an add switch

This adds another check to issue #12.  One step closer!
Add shouldn't exit on add failure

Just because one file is already in hermit doesn't mean everything else
is.
Remove the redact command
Add a test for redaction
Ensure that ed is on the travis machine