Cassette.jl backend

[cstjean]

@jrevels I'm growing increasingly dissatisfied with my current tracing procedure (mostly that it's slow to parse all of these source files), and Cassette.jl looks super-promising 👍. Is there any limitation that I should know about with regards to generating traces like I have in the manual? For instance, will you be able to nicely handle keyword arguments and generated functions? Is there a way to only trace the functions in some module M? Do you have any inside knowledge on whether JuliaLang/julia#5402 is given priority?

I'm asking because I have a third option, which is to use code_lowered to get the code from each method, then use eval to temporarily replace those functions (as I am doing now). It's potentially a lot of work. Depending on the timeline for a viable Cassette.jl backend, I might code it up...