fix CRC algorithm in WAL reliability docs

I noticed that the "WAL reliability" documentation says that we use CRC-32
for WAL records and two-phase state files, but we've actually used CRC-32C
since v9.5 (commit 5028f22).  I've attached a short patch to fix this that
I think should be back-patched to all supported versions.

I've attached a second patch that standardizes how we refer to these kinds
of algorithms in our docs.  Specifically, it adds dashes (e.g., "CRC-32C"
instead of "CRC32C").  Wikipedia uses this style pretty consistently [0]
[1] [2], and so I think we should, too.  I don't think this one needs to be
back-patched.

Thoughts?

[0] https://en.wikipedia.org/wiki/SHA-1
[1] https://en.wikipedia.org/wiki/SHA-2
[2] https://en.wikipedia.org/wiki/Cyclic_redundancy_check

-- 
nathan