Generally try to make this more comprehensible, and make it match the
conventions.
I've removed the documentation for all the settings which allow you to change
the names of the template files, because I can't really see why they are
useful.
The general idea here is that config examples should just have a hash and no
extraneous whitespace, both to make it easier for people who don't understand
yaml, and to make the examples stand out from the comments.
The redact_content option never worked because it read the wrong config
section. The PR introducing it
(https://github.com/matrix-org/synapse/pull/2301) had feedback suggesting the
name be changed to not re-use the term 'redact' but this wasn't
incorporated.
This reanmes the option to give it a less confusing name, and also
means that people who've set the redact_content option won't suddenly
see a behaviour change when upgrading synapse, but instead can set
include_content if they want to.
This PR also updates the wording of the config comment to clarify
that this has no effect on event_id_only push.
Includes https://github.com/matrix-org/synapse/pull/2422
