Pkg3: naming of project filenames

Hi all

I saw the [talk on Pkg3](https://www.youtube.com/watch?v=-yUiLCGegJs) and was a bit confused with the naming.
My personal expectation was something like this:

* `Manifest.toml` for the actual configuration
* `Manifest.lock` for the latest working set
* `Manifest.journal` for the log. This one I would expect to be a like [firebird](http://firebirdsql.org/) or another single file db with a lock.

Of course `Config.*` would be fine too. The mix of `Config.toml` and `Manifest.toml` was confusing me since many develop environments use them also.
Like android with `Manifest.xml` or npm with `packages.json` and `packages-lock.json` or cargo with `Cargo.toml` and `Cargo.lock`.

Regards

Start by reading the Pkg3 naming discussion and comparing the proposed Manifest.toml, Manifest.lock, Manifest.journal, and Config.* names with the existing convention. Review the examples from Android, npm, and Cargo, then determine whether a settled filename scheme is possible; done means an agreed naming decision rather than a localized code edit.

Written by the indexing model from the issue text.