Add more built-in functions

[amterp]

Am continuing to build out rad's library of functions. Pretty easy to do, see f64d88c as an example.

Feel free to suggest. Some ideas:

• divmod
• repeat for repeating strings, or otherwise have some syntax like "a" * 5

[gnana997]

Hi @amterp , Can I take look into this and work on it?

[gnana997]

Hi @amterp , Actually I started working on this before messaging here. So I still pushed my changes. Let me know if I should proceed with writing the test cases.

[amterp]

Responded on the PR, thanks @gnana997 !

[gnana997]

Hi @amterp , can you assign the issue to me and close this issue as the pr is merged.
Thanks

[amterp]

Hey @gnana997, I'll keep this one around since those added in #5 were just some suggestions that came to mind at the time - the list of builtin functions we need in RSL is no doubt incomplete and so it remains a task to add more :)

In future I might indeed raise a subtask first though, if specific functions are committed to!