API improvements

## Description

Refine the API props and options for Leonardo to be more intuitive and consistent.

Considering there are other tools out there (including the d3 and chroma.js libraries) that have similar options, conforming to similar prop names or casing styles would make this tool more intuitive for consumers who are familiar with those tools.

For example:
- Lower case colorspace names: 'lch' instead of 'LCH'
- `colorspace` prop should either be camel case, or use a more literal term like `interpolate`/`mode`
- `output` may be better surfaced as `format` (eg, d3 `formatRgb`)

Overall evaluation and comparison of prop names and values should be done beyond those examples.

## Why do you need this feature?

Solidify the API for Leonardo by relating to existing language, props, and values expressed in other similar tools or industry standards.

## Leonardo package and version

## Additional context

Start by locating Leonardo's current public props and option definitions, then compare their names, casing, and values with the d3 and chroma.js conventions mentioned in the issue. Done means the API naming and value conventions have been evaluated and a consistent direction is agreed for the full set of options, not just the examples listed.

Written by the indexing model from the issue text.