Proxy touchup

[fluvf]

Based on #45

• Turns crel into a proxy, allowing for a shorter calls: crel.div()
  Also makes crels internal structure cleaner, as bound functions are cached in crel.proxy
• Adds tag / key transformations, Proxy case conversion #28
• Turns crels handler function into an arrow function
• Adds appropriate tests
  The best size saving change after this would be removing support for crel.proxy.div() calls

I also have some large changes to how tests are run, removing separate tests for normal function calls and proxies, instead using existing tests for both.
But as it's rather large (and maybe a bit overkill), I'll do one last pr