I find excluding -999.0 values annoying in practice.

example:

```
let a: Option<d128> = Some(d128::from_str("123.456").unwrap());
let b: Option<d128> = None;
measure!(influx, meas, D(a), D(b));
```

in the `None` case, no field is added at all.

- adds example to repeatedly send many measurements to InfluxWriter for purposes of stress testing (i.e. shut influxdb off, see if InfluxWriter recovers correctly)
- InfluxWriter now tracks allocated buffer memory and logs it
- lower INITIAL_BACKLOG

allows optional compression on rotated logfiles

this thing is a fucking rock now

will need extensive testing before prod use

- `v`: adds a tag "version" based on the expression, e.g. `v(VERSION)`
-> `t("version", VERSION)`
- `utc`: like `tm`, but converts a `DateTime<Utc>` to `i64`
automatically

this was to test cost in terms of compilation speed. doesn't seem like a
big deal but leaving it in case it is later.

I copied several Window structs from windows crate to avoid a cyclic
dependency. The rationale was, latency mod is on its way out anyway.