this is for supporting external plugins.
external plugins will depend on a few telegraf interface types, as well
as a common telegraf registry.
this will allow external and internal plugins to both share this package
and make it easier to vendor/version the whole thing semantically, which
will make it easier to keep plugins supported across build and telegraf
versions.
see #1717
1. in prometheus client, do not check for invalid characters anymore,
because we are already replacing all invalid characters with regex
anyways.
2. in win_perf_counters, sanitize field name _and_ measurement name.
Also add '%' to the list of sanitized characters, because this character
is invalid for most output plugins, and can also easily cause string
formatting issues throughout the stack.
3. All '%' will now be translated to 'Percent'
closes#1430
percentage characters in sampleConfig string so that fmt.Printf
will interpret them as literal percentage characters when
running 'telegraf.exe -sample-config'
closes#620
Cameron Sparr
Pierre Fersing
Jeff Ashton
Da1den
G-regL
Rune Darrud
Christoph Wegener