update Dockerfile and fix root build error (see MLton#601)

update readme for v0.5.2

README updates

wording tweaks for readme, and mention mpl-switch install v0.5

attempt at tuning payout

bugfix: clear wsqueue when return to sched

Merge pull request #173 from MPLLang/prep-v0.4-release

(WIP) v0.4 release

two-gpu test

MPL version 0.3

release notes typo