downsample 0.0.4

keep downsampled history of data over long period of time
Documentation 
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# downsample

no-std library to downsample fixed-frequency or time-based metrics for long history storage.

Let's assume you have a temperature sensor that can do 100 measurements per second and stores the data in a `f32`.
You want to keep track of some historic samples, like from last year, but you don't need them at the same 100Hz as your raw data as `365 * 24 * 60 * 60 * 100 * 4byte = 12GB` is just to much data.

Alternativly it will provide a time-based downsampler where you can store data in levels with no fixed size but a fixed interval.
time-based downsampling is not yet implemented.

# Usage

```rust
use downsample::FixedFrequencyBuilder;
use rand::Rng;

fn main() {
    // 0s - 1s : 100Hz
    // 1s - 1m : 1Hz
    // 1m - 1h : 1/60 Hz
    // 1h - 1d : 1/3600 Hz
    let mut temperature_measurements = FixedFrequencyBuilder::new(100, 100)
        .level(59, 100)
        .level(59, 60)
        .level(23, 60)
        .build();
    for _ in 0..1000 {
        temperature_measurements.push(rng.gen::<f32>());
    }
}
```

# Limitations

- Bucket size must be known on creation of the object.
- Only whole numbers are allowed as a downsample factor. e.g. 100Hz -> 25Hz -> 5Hz is possible with factor 4 and 5, but 100Hz -> 25Hz -> 10Hz isn't as factor 2.5 is no integer.

# Early release version

This crate is in version `0.0.x` that means the api will change rapidly, traits will change nothing is even nearly stable yet