Fixes #7144.

As using non-C locale can cause issues on upgrading OS.

Ensure that the the default settings for the room directory are that the it is hidden from public view by default. 

another typo

fix typo

 * make it clear that if you installed from a package manager, you should use
   that to upgrade

 * Document the new way of getting the server version (cf #4878)

 * Write some words about downgrading.

Converting some of the rst documentation to markdown.  Attempted to
preserve whitespace and line breaks to minimize cosmetic change.

Allow Synapse to send registration emails + choose Synapse or an external server to handle 3pid validation (#5987)

This is a combination of a few different PRs, finally all being merged into `develop`:

* #5875 
* #5876 
* #5868 (This one added the `/versions` flag but the flag itself was actually [backed out](https://github.com/matrix-org/synapse/commit/891afb57cbdf9867f2848341b29c75d6f35eef5a#diff-e591d42d30690ffb79f63bb726200891) in #5969. What's left is just giving /versions access to the config file, which could be useful in the future)
* #5835 
* #5969 
* #5940

Clients should not actually use the new registration functionality until https://github.com/matrix-org/synapse/pull/5972 is merged.

UPGRADE.rst, changelog entries and config file changes should all be reviewed closely before this PR is merged.

1.0 upgrade/install notes

See: https://en.wiktionary.org/wiki/successful

MSC1711 certificates FAQ

* Remove --process-dependency-links from UPGRADE.rst

Signed-off-by: Aaron Raimist <aaron@raim.ist>

* Add changelog

Signed-off-by: Aaron Raimist <aaron@raim.ist>

This is based on the work done by @krombel in #2601.

* Add note to UPGRADE.rst about removing riot.im from list of trusted identity servers

Signed-off-by: Aaron Raimist <aaron@raim.ist>

* Add changelog

Signed-off-by: Aaron Raimist <aaron@raim.ist>

This fallback didn't work, and was removed in #4069.

We aren't ready to release this yet, so I'm reverting it for now.

This reverts commit d1679a4e, reversing
changes made to e089100c.

This requires the psutil module, and is still opt-in based on the report_stats
config option.