Update accepted format

[wysiwys]

This draft pull request updates the formats accepted by this action, in order to allow for more flexibility and provide more granular control over the keys in each benchmark.

• Allow unit to include 'μ' character in cargo input
• Allow range to be missing in cargo input
• Accept key-value pairs as a list of (key=value) items

It also updates tests and test data to take these changes into account, and additionally updates all of the examples and tests to output to a file with the .json extension rather than one with the the .txt extension.

[keks]

Looks good, thanks!