Fixing up edge cases with influxdb's new line protocol

[timgriffiths]

Based on the spec https://influxdb.com/docs/v0.9/write_protocols/write_syntax.html

I am just implementing this rule

Escaping Characters
If a tag key, tag value, or field key contains a space , comma ,, or an equals sign = it must be escaped using the backslash character \. Backslash characters do not need to be escaped. Commas , and spaces will also need to be escaped for measurements, though equals signs = do not.

Let me know if you want more unit tests