Optimizes int types for in memory storage

[dwjbosman]

When having large arrays of a type that has a small range, the code generator should use the correct integer type to avoid wasting precious memory.

Fix for #459

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
2 out of 3 committers have signed the CLA.

✅ oyvindronningstad
✅ dwjbosman
❌ Dinne Bosman

---

Dinne Bosman seems not to be a GitHub user. You need a GitHub account to be able to sign the CLA. If you have already a GitHub account, please add the email address used for this commit to your account.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[dwjbosman]

I have not been able to run the tests!

[oyvindronningstad]

Thank you!

One line length issue (see comment). Also, please rebase your branch to a single non-merge commit

[oyvindronningstad]

@dwjbosman Thanks for your contribution! I have taken your code and made a number of fixes and improvments to it, which you can find at #466. Feel free to grab that commit into this PR, and possibly add you own Signed-off-by line (git commit --amend -s). The commit is based on your work and is in your name as author. If I don't hear from you I will put myself as author so as not to impersonate you, and instead credit you in the commit message.