0.8

CHANGES:

• api(fut): make alias 'a Fut.t = 'a Picos.Computation.t public

• feat: add Fut.make_promise, have 'a promise = private 'a fut

• feat(exn_bt): in show/pp, do print the backtrace when present

• feat: block signals in workers if asked to

• relax bound on picos to 0.5-0.6

• feat fib: spawn_ignore now has ?on optional param

• change Moonpool.Chan so it's bounded (stil experimental)

• fix task local storage: type was too specific

• fix fiber: use a single fut/computation in fibers