Package Agda 2.6.4

[andreasabel]

Would be great if Agda 2.6.4 was supported. Standard libraries 1.7.1/2 work mostly with Agda 2.6.4, but some modules do not build because they would need --large-indices.
Maybe you want to await 1.7.3 of the library, although installing Agda without the library also has uses.

Update: @MatthewDaggitt just released 1.7.3 of the standard library!

[wenkokke]

My eventual plan is to deprecate this action in favor of a much simpler action which installs agda-python, due to the ease of maintenance: It's much less code, and gets distribution via PyPI for free!

My only concerns are:

• The Python distribution does not support cluster counting on all platforms.
• The Python distribution does not support installing libraries.

I'm looking into solutions for the former. (Ultimately, I believe we should drop the dependency on text-icu.)

The latter, I believe, should be solved by the Agda project, e.g., by supporting an agda pkg install command such that agda pkg install <url to archive> downloads and extracts the archive and adds it to the libraries file.

However, I'm happy to continue supporting the next few releases.

[wenkokke]

This should be working now :)