closes #1726

in this commit:

- centralize logging output handler.
- set global Info/Debug/Error log levels based on config file or flags.
- remove per-plugin debug arg handling.
- add a I!, D!, or E! to every log message.
- add configuration option to specify where to send logs.

closes #1786

* convert postgresql_extensible byte slice values to strings

* code cleanup in postgresql_extensible

Allow overriding the the metrics "server" tag with the specified
value. Can be used to give a more user-friendly value for the server
name.

closes #1093

nil field values would break the output influxdb line procotol.
Skip them from the output.

The output measurement name can be configured per query.

While these aren't quite as sensitive as passwords, they do tend to be
long filesystem paths that shouldn't be reported along with
every measurement.

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

closes #844

This plugin is intended to add an extended support of Postgresql
compared to the legacy postgres plugin.

Basically, the plugin don’t have any metrics defined and it’s up to the
user to define it in the telegraph.conf (as a toml structure).

Each query can have it’s specific tags, and can be written specifically
using a where clause in order to eventually filter per database name.

To be more generic, a minimum postgresql version  has been defined per
query in case you have 2 different version of Postgresql running on the
same host.