Consider removing "project" variable

[vsoch]

As discussed in #6 (review) with @Beanow, we could very easily remove the need to specify a project identifier (the project action variable) that is needed to run sourcecred scores if we can parse it directly from the file. Some points to think about:

• the project id would likely always be supported in the action, and used if the user provides it (and we would skip parsing)
• if no project id is provided and the file just has one, we can use what we find when we parse
• if no project id is provided and more than one are found, we would need to throw an error.

This likely won't go into the first round of edits, as I think it requires more work/ discussion (or maybe me just knowing about) the format for this project file. But definitely let's keep it on the radar for the future.

[Beanow]

Seeing how this is fairly inconsistent in the SourceCred CLI (and that's a clear smell), I would not put too much work into a permanent solution in the action. It will likely be changed in SC itself.

My preference for the next SC release would be to move to a notion of "SourceCred instances" where there is always exactly 1 project. Meaning the ID for projects becomes obsolete.

Though, because it would become obsolete, I do suggest trying to create the action's interface with exactly 1 project in mind. So removing the ID from the arguments if we can easily do so would be great :]