Add pg_settings for versions 9.3-9.6

[andreif]

Min/max wal size part is taken from
https://github.com/le0pard/pgtune/blob/master/source/javascripts/pgtune.coffee#L132-L155

On macOS I was testing with

$ export lib="/Users/andrei/Library/Application Support/Postgres"

$ python pgtune --version=9.4 --input-config="$lib/var-9.4/postgresql.conf" --type=Web

$ python pgtune --version=9.5 --input-config="$lib/var-9.5/postgresql.conf" --type=Web

$ python pgtune --version=9.6 --input-config="$lib/var-9.6/postgresql.conf" --type=Web

[andreif]

You can also try andreif@allthethings which contains #16, #18 and some other fixes.

[andreif]

@Phone911 Thanks, maybe somebody has time to confirm it or I could do it whenever I find time for it.

[OriginalPenguin]

@andreif

I'm using your fork now. It's very helpful. Thank you.

Would you consider updating it for Postgres 11?

Also would you consider turning issues on for your fork? They seem to be turned off.

Thanks