Frequency Distribution

Provides a Frequency Distribution data structure, which can keep track of the number of times an object appears in some context.

Example

```rust use freqdist::{Distribution, FrequencyDistribution};

let mut fdist = FrequencyDistribution::new();

fdist.insert("hello"); fdist.insert("hello"); fdist.insert("goodbye");

assert_eq!(fdist.get(&"hello"), 2); ```