Function stream

stream(minDefault?: number, maxDefault?: number): (v: number) => number
Normalises numbers, adjusting min/max as new values are processed. Normalised return values will be in the range of 0-1 (inclusive).

ixfx Guide on Normalising
Parameters
- OptionalminDefault: number
- OptionalmaxDefault: number
Returns (v: number) => number
Example
```
import {Normalise} from 'https://unpkg.com/ixfx/dist/numbers.js'
const s = Normalise.stream();
s(2);    // 1 (because 2 is highest seen)
s(1);    // 0 (because 1 is the lowest so far)
s(1.5);  // 0.5 (50% of range 1-2)
s(0.5);  // 0 (because it's the new lowest)
```
Since normalisation is being adjusted as new min/max are encountered, it might be that value normalised to 1 at one time is different to what normalises to 1 at a later time.

If you already know what to expect of the number range, passing in minDefault and maxDefault primes the normalisation.
```
const s = Normalise.stream();
s(5); // 1, because it's the highest seen

// With priming:
const s = Normalise.stream(0, 10);
s(5); // 0.5, because we're expecting range 0-10
```
If a value exceeds the default range, normalisation adjusts. Errors are thrown if min/max defaults are NaN or if one attempts to normalise NaN.