Rename *SSL* settings to *TLS*

[Hugo Osvaldo Barrera]

After searching through the documentation for a few TLS related settings, I
failed to find anything. A while later, I found them as *SSL*.

I'd like to suggest renaming settings that mention SSL to TLS, to reflect that
the former is now deprecated.

eg: SECURE_PROXY_SSL_HEADER -> SECURE_PROXY_TLS_HEADER

This should improve the ability for new users to find these settings, and
reflect current practices (eg: that SSL has been completely deprecated in
favour of TLS).

Any opinions or complaints to this?

--
Hugo Osvaldo Barrera
A: Because we read from top to bottom, left to right.
Q: Why should I start my reply below the quoted text?

[Collin Anderson]

I don't think it's really worth changing, but if anything, I'd recommend HTTPS rather than TLS, as that doesn't care about the underlying protocol which may change again in the future. Or maybe go with PROXY_SCHEME_HEADER or something.