Show setting defaults as actual code

For some reason, setting names on the Settings page have long been
wrapped in single back-ticks (usually meant for linking in reST) instead
of double back-ticks (meant for denoting code). This seems to be
widespread throughout the docs, and it's not clear if this is
intentional or simply a reST formatting error that got propagated by
others in order to stay consistent. This commit applies double
back-ticks in any case where something resembling code is shown, with
the idea that single back-ticks should only be used when linking.

More importantly, the settings denoted their default values in
parentheses, which hapless users often included when copying and pasting
these values into their config files. As one can imagine, confusion —
not hilarity — ensued. Setting defaults are now shown as they would
actually appear in one's settings file, with an equal sign and without
parentheses.

During this spelunking expedition, many other minor improvements were
concurrently conducted.