Add missing parameters for 1.4.0 release

This patch adds all the missing parameters now defined in the 1.4.0 release.

This includes some new database parameters mainly, but also adds gc_interval
to the `puppetdb` and `puppetdb::server` classes, as previously this wasn't
configurable using this method.

To avoid documentation duplication the Puppet headers have been removed in
favour of documenting classes from the README.md. Until such times as the
forge can turn Puppet docs into HTML automatically, this is just duplicate
noise and prone to update slippage. The README.md is more authoritative in
this area and is pubicly displayed on the forge project page so it should be
used for now.

Signed-off-by: Ken Barber <ken@bob.sh>
Merge pull request #76 from kbarber/missing_config_params

Add missing parameters for 1.4.0 release
Release 1.6.0

Updates CHANGELOG and the Modulefile for the next release.

Signed-off-by: Ken Barber <ken@bob.sh>
Provide the PuppetDB version that the new parameters apply for

This documents each of the newer parameters: gc_interval, log_slow_statements,
conn_max_age, conn_keep_alive, conn_lifetime with the version of PuppetDB that
are supported on.

Signed-off-by: Ken Barber <ken@bob.sh>
Merge pull request #77 from kbarber/release_160

Release 1.6.0