Add leex/heex to projectionist

[zolrath]

This adds the html.leex/html.heex files to projectionist. Only odd part on this is that we can't have multiple alternates so :A will jump to the test which will jump back to the .ex file.

Alternatives/Questions

• We could have the alternate file be the .ex file instead of the test.
• Do we want a basic ["<div>", "", "</div>"] template or just leave it blank?

Usage

Due to the ambiguity these would mostly be used via :Eleex and :Eheex to switch to the file or create it if it does not exist.

[mhanberg]

@zolrath when https://github.com/elixir-tools/elixir-tools.nvim/pull/108 merges, you should have a foundation for adding projectionist tests.

you can run the tests with bin/test or bin/test path/to/file.

You should run this with >= 0.9 for it to work well.

I'm copy pasting this comment to your other PR

[mhanberg]

Only odd part on this is that we can't have multiple alternates

I think you can

                        *projectionist-alternate*
"alternate"  
        Determines the destination of the |projectionist-:A| command.  If this
        is a list, the first readable file will be used.  Will also be used as
        a default for |projectionist-related|.

[mhanberg]

@zolrath let me know if you can get to this in the next week or so. if you can, i'll wait to cut the next release, but if not, i'll cut it and this can go in the next one