Changed Hack Collections with Hack Arrays

[CarusoX]

Replaced:

• Vector, ImmVector with vec
• Map, ImmMap with dict.

Updated the needed documentation on the README.

[CarusoX]

I had to add the hsl-experimental prior version, since some project packages still need that version to work (due to the \Experimental\ being removed)

[fredemmott]

The HHAST errors need a new release of HHAST with the new schema; you also need to adjust .travis.yml for the new minimum version

[fredemmott]

Sorry, just meant that the new release had to actually be released; this should be automatically picked up based on hhast's own version requirements, now that it's happened.

[lexidor]

Sorry for waking this PR from its slumber. This PR has merge conflicts.

Would you mind if I took your changes and redid this collection -> array migration? How would you like to be credited / get attribution for your work? Would you like a Co-authored by mention? This might imply you agree with my changes though, so that's why I felt I had to ask before doing so.

If you've moved on or are unable to reply for any reason, I'll use a with great thanks to CarusoX instead.

[CarusoX]

Sound fine to me @lexidor! Thanks for the mention!