* Add configuration docs to Postgresql input plugin

Add configuration docs to PostgreSQL input plugin README (mostly from the source code) though I've not included the configuration example that seems to use all he connections on the database[1].

[1] https://github.com/influxdata/telegraf/issues/2410

* Fix typo in readme and sampleConfig string.

that handles them properly

* separate hello and authenticate functions, force connection close at end of write cycle so we don't hold open idle connections, which has the benefit of mostly removing the chance of getting hopelessly connection lost

* update changelog, though this will need to be updated again to merge into telegraf master

* bump instrumental agent version

* fix test to deal with better better connect/reconnect logic and changed ident & auth handshake

* Update CHANGELOG.md

correct URL from instrumental fork to origin and put the change in the correct part of the file

* go fmt

* Split out Instrumental tests for invalid metric and value.

* Ensure nothing remains on the wire after final test.

* Force valid metric names by replacing invalid parts with underscores.

* Multiple invalid characters being joined into a single udnerscore.

* Adjust comment to what happens.

* undo split hello and auth commands, to reduce roundtrips

* Add ignored_databases option to postgresql configuration files, to enable easy filtering of system databases without needing to whitelist all the databases on the server.  Add tests for database whitelist and blacklist.

* run go fmt on new postgresql database whitelist/blacklist code

* add postgresql database blacklist option to changelog

* remove a bad merge from the changelog

changes:

- -sample-config will now comment out all but a few default plugins.
- config file parse errors will output path to bad conf file.
- cleanup 80-char line-length and some other style issues.
- default package conf file will now have all plugins, but commented
  out.

closes #199
closes #944

Fix the password exposure in the metrics or tags.

closes #821
closes #845

Add pg_stat_bg_writer stats

closes #683

closes #599

This will basically make the root directory a place for storing the
major telegraf interfaces, which will make telegraf's godoc looks quite
a bit nicer. And make it easier for contributors to lookup the few data
types that they actually care about.

closes #564