Planned features

A tracking issue for planned features of Linefeed.

- [x] _Everything_ is an expression
- [ ] Lazy keyword
- E.g. `lazy foo = 1 + 2` is not evaluated until first use
- [ ] (Linear-algebraic) vectors
- [x] By-default big integers (as in Python, Perl, and Ruby)
- [ ] Good I/O tooling
- [ ] Null file handle (as in Perl's null file handle)
- [x] Regex support
- [x] Trait-based
- [x] Dictionaries with any key, for example
- [x] Operators: addition for strings, numbers, vectors etc

_... and more_

And some "might be fun but might not happen" features:

- [ ] Make a JIT compiler that uses LLVM
- [ ] Type inference
- [ ] Linear algebra: matrix multiplication, determinants, inverse

## Discarded features
- ~~Nullish coalescing operator~~. Can be done with the `or` operation most of the time. Abandoned for now.
- ~~Complex numbers~~. Add linear-algebraic vectors instead with useful methods. In Python, complex numbers were used as a stand-in for vectors 99% of the time (in my case).