Add a `coverage` export that gets the code coverage of a particular module

[Vehmloewff]

This can be done by running deno test with the --coverage option. You can then get a doc view of the target module, determine which files are included, and, if they are not in the coverage, include those with a coverage of 0%.

Advanced
Do this all on a function/by/function basis

[Vehmloewff]

Some starter code I wrote in a coverage.ts file:

export async function getCoverage(entryPoint: string): Promise<void> {
	const files = await readDir('code_cov')

	for (const file of files) {
		const contents = await readJson(pathUtils.join('code_cov', file))
		if (!contents.url.startsWith('file://')) continue

		for (const func of contents.functions) {
			console.log(contents.url, func)
		}
	}
}

await getCoverage('foo')