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
Network metrics are pretty important and the block adds a couple with a link to the names for more. This adds a block with a few counters to the Generic Queries examples in plugins/inputs/win_perf_counters/README.md
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
G-regL
Martin Gehrke
Rune Darrud
Christoph Wegener