fix: added missing keywords for highlighting

[rroutsong]

A lot of missing keywords for snakemake highlighting. Just added into 0.4.0 token lists.

Addresses some or all of issues #23, #18, #14, #22, #25

[corneliusroemer]

Oh you beat me to it, I opened #31 before seeing this. You're still missing 'retries'

[corneliusroemer]

Easier to review if you just change this one file: https://github.com/snakemake/snakemake-lang-vscode-plugin/pull/24/files

[rroutsong]

No worries, I am sure I missed a few more too I couldn't find a good extensive list of all keywords and their support or deprecation by version.

[corneliusroemer]

Oh damn, I might be wrong, PR #24 doesn't seem to fix syntax highlighting. Have to dig a bit deeper, but thanks for giving this a go. We should figure out how to test it, that'd be useful!

[rroutsong]

OK I am not so familiar with VScode extension development, so I might have borked it up. But I made this into a local vsix and distributed it to my group and it worked for our highlighting purposes.

[mbhall88]

pepfile and pepschema also seem to be missing. Could you also add that to this PR?

[rroutsong]

pepfile and pepschema also seem to be missing. Could you also add that to this PR?

added