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