Documentation fixes

[fredericDelaporte]

Remove references to an obsolete configuration section since NHibernate 2.0.0 (NH-1087), and clarifies system-level properties.

Fixes #1386.

[fredericDelaporte]

The cache settings are documented as of NHibernate.Caches 5.1.0, which I intend to publish soon (now published).

[hazzik]

bet?

[fredericDelaporte]

Oops...

[fredericDelaporte]

No bet anymore.

[fredericDelaporte]

Rebased, some more typo fixed, backported css changes.

[hazzik]

@fredericDelaporte I think the PRs need to be as targeted as possible (eg, try to fix one issue at a time)

[fredericDelaporte]

I tend to group by subjects (here a bunch of documentation fixes) due to those factors:

• Builds are long. We have currently more than 24h of builds queued according to TeamCity. Each PR triggers its build, while commits grouped in a PR may not do that (if not pushed one by one with waiting for the build to start on each).
• Stale PR merges are blocked, so we have to update them at each merge of other PR (or use admin privilege). The more we have PR, the more updates we do on them, the more builds we add.

Having separated commits still allows to distinguish the sub-subjects.

Doing 4 to 6 PR instead of this single one looks to me as a bit overkill for those documentation fixes.

[ngbrown]

Maybe the TeamCity server could skip all the per-db-server tests if the changes are just documentation. This could be done with VCS trigger rules. The GitHub "Required" tests may have to be scaled back to prevent merges from being blocked.

[hazzik]

I've excluded doc/** from the DB builds as @ngbrown suggested

[fredericDelaporte]

Thanks for the fixes, rebased and squashed.