Support for macros and other 'nice' instructions such as `NOP`, and labels/data/etc...

The assembler is kinda barebones, would be good to add support for:

- Macros
- nice instructions such as `nop` which decomposes into `add x0 x0 x0` for eg. (Probably via macros)
- Label for jumps (automatically figure out the offset/addressing needed
- A way to set aside a region for data, and a region for code