Prefixed

**Changes**
- The micro symbol ('µ'), U+00B5, is now accepted as a valid prefix when creating ``prefixed.Float`` objects from strings
- Output will still use the lowercase Greek letter mu ('μ'), U+03BC
- This complies with the preference defined in [Unicode Technical Report 25](https://www.unicode.org/reports/tr25) section 2.5
- A note was added to the documentation for reference

- Bugfixes
- Rounding was not accounted for when determining prefixed
- For example, `f'{Float(9.999999999e-10):.2H}'` returned `1000p` rather than `1n`
- Rounding is now accounted for when determining prefix

**Housekeeping**
- Metadata updates

**Changes**
- Magnitude values are read from a dictionary rather than computed
- This should result in faster and more consistent behavior

**Changes**
- Consistent behavior for `!` flag
- The `!` flag used to drop the space when no prefix was added to the output
- This created issues in cases like `f'{Float(123):!.3H}J'` 4
- `!` will now always add a space after the number

- New flag `!!`
- The new flag `!!` operates like `!`, adding a space between the number and the prefix
- `!!` will drop the space if no prefix is added to the number
- See the [documentation](https://prefixed.readthedocs.io/en/stable/format_spec.html#flags) for more information

**Changes**
- Add new SI prefixes
- [Added at November 2022 General Conference on Weights and Measures](https://metricviews.uk/2022/11/20/first-new-si-prefixes-for-over-30-years/)

| Prefix | Name | Base |
| --------- |---------- | ----- |
| Q | quetta | 10³⁰ |
| R | ronna | 10²⁷ |
| r | ronto | 10⁻²⁷ |
| q | quecto | 10⁻³⁰ |

**Bugfixes**
- In some circumstances significant digits were one decimal place off
- Caused by floating point variance
- Value is now constrained prior to determining significant digits