add an scm rockspec

[leafo]

This adds a rockspec that can build from the master branch of the source repository. In this convention we check this rockspec in because it can be used universally. Generally versioned rockspecs you don't check in.

This will enable someone to build and install the latest version via LuaRocks with a command like:

luarocks install https://raw.githubusercontent.com/lgi-devs/lgi/master/lgi-scm-1.rockspec

After this change is accepted, we can also upload the scm rockspec to luarocks.org so we can use the "dev" manifest to also install the development version of this module

[Frityet]

It doesn't seem that the scm rockspec is the same that is uploaded to the luarocks.org/dev server, is this intentional?

@psychon

[psychon]

Dunno what you mean exactly, but according to https://luarocks.org/modules/pavouk/lgi, pavouk last uploaded something 6 years ago, but this PR is only one year old, so obviously newer than that.

[Frityet]

Oh, I just realized there is no dev upload for lgi in general, could that be considered? It would allow the latest source release of lgi to be installed with luarocks install --server=https://luarocks.org/dev lgi

[psychon]

Well, feel free to do that. You are in a better position to do that than I am since you apparently use luarocks and understand how it works. According to https://github.com/pavouk?tab=overview&from=2015-11-01&to=2023-11-18, pavouk was last active eight years ago, so I wouldn't expect that he uploads something there.