Add more types: Floats, Structs and stuff

[chsasank]

Add floating point types

https://capra.cs.cornell.edu/bril/lang/float.html

and tests:

https://github.com/sampsyo/bril/tree/main/test/interp/float

Look up how do we add char and stuff too

[chsasank]

The types we need to implement:

1. Floats
2. Structs
3. Arrays

In that order of priority. See #16 for interesting discussion on array type vs alloc

[chsasank]

Aggregate types in LLVM are documented here: https://llvm.org/docs/LangRef.html#t-aggregate

[GlowingScrewdriver]

Structs will have to be implemented in Brilisp and C-Lisp. As with the other features, Brilisp structs will mirror LLVM structs, and C-Lisp structs will extend that to provide something more typical of a high-level language.

Tentative design decisions for Brilisp structs:

• No element names, only indices (as with LLVM)
• Structs will be allocated in memory using alloc and accessed through pointers only, just like arrays
• No nested structs

[GlowingScrewdriver]

This is done, right?

[GlowingScrewdriver]

Ah, yes. We still don't have characters.

[chsasank]

Partly resolved by #68