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.