sail-to-lean: project milestones

[tobiasgrosser]

• support the sail prelude
• https://alasdair.github.io/manual.html#_a_tutorial_risc_v_style_example
• https://github.com/rems-project/sail-tiny-arm

[jprider63]

@javra is planning to go through these early models and start creating issues that breaks down which AST elements need to be implemented. If you start working on one of these, assign the issue to yourself so that multiple people don't work on the same one.

[javra]

examples/riscv-dupod.sail actually doesn't compile right now, for some reason it complains about a "Redundant wildcard clause"