v0.5.0

It's been far too long since I've done a release and we have a lot of accumulated changes.

* Docker image now runs as a non-root user named "postgres_exporter"
* Add `--auto-discover-databases` option, which automatically discovers and scrapes all databases.
* Add support for boolean data types as metrics
* Replication lag is now expressed as a float and not truncated to an integer.
* When default metrics are disabled, no version metrics are collected anymore either.
* BUGFIX: Fix exporter panic when postgres server goes down.
* Add support for collecting metrics from multiple servers.
* PostgreSQL 11 is now supported in the integration tests.

v0.4.7

* Added a query for v9.1 pg_stat_activity.
* Add `--constantLabels` flag to allow applying fixed constant labels to metrics.
* queries.yml: dd pg_statio_user_tables.
* Support 'B' suffix in units.

v0.4.6

* Fix issue #173 - 32 and 64mb unit sizes were not supported in pg_settings.

v0.4.5

* Add commandline flag to disable default metrics (thanks @hsun-cnnxty)

v0.4.4

* Bugfix for 0.4.3 which broke pg_up (it would always be 0).
* pg_up is now refreshed based on database Ping() every scrape.
* Re-release of 0.4.4 to fix version numbering.

v0.4.2

* Adds the following environment variables for overriding defaults:
    * `PG_EXPORTER_WEB_LISTEN_ADDRESS`
    * `PG_EXPORTER_WEB_TELEMETRY_PATH`
    * `PG_EXPORTER_EXTEND_QUERY_PATH`

* Add Content-Type to HTTP landing page.
* Fix Makefile to produce .exe binaries for Windows.

v0.4.1

* No code changes to v0.4.0 for the exporter.
* First release switching to tar-file based distribution.
* First release with Windows and Darwin cross-builds.\\

v0.4.0

* Fix panic due to inconsistent label cardinality when using queries.yaml with
  queries which return extra columns.
* Add metric for whether the user queries YAML file parsed correctly. This also
  includes the filename and SHA256 sum allowing tracking of updates.
* Add pg_up metric to indicate whether the exporter was able to connect and
  Ping() the PG instance before a scrape.
* Fix broken link in landing page for `/metrics`

v0.3.0

* Add support for PostgreSQL 10.

v0.2.3

* Add support for the 16kB unit when decoding pg_settings. (#101)