Policy: A deprecation policy

[r0ml]

Over time parts of the HP will become obsolete.

We need to pick a deprecation and removal policy.

e.g. add deprecation flags once a replacement is added. Hold for 2 years, then remove.

[r0ml]

Did you mean 'e.g.' rather than 'i.e.' there? ('e.g.' would be giving an example policy, 'i.e.' would be stating that it should be a certain thing)