Leave tools team, join HAL, libs and embedded Linux teams.

[reitermarkus]

I initially joined the tools team to maintain cross, which isn't in this org anymore and I am not really using the other tools. I mostly use heapless, embedded-hal, critical-section and the various embedded Linux crates these days, and it makes sense to maintain the crates I actually use.

[therealprof]

Would you mind splitting this up into multiple PRs to simplify the voting which has to happen per team?

[adamgreig]

Thank you for all your help with cross!