Parallel tasks break progress bar output

[dmcilvaney]

Need a way to squelch log output when running in parallel so progress bars work. Maybe provide a log interface from Env that can be configured by creating a nested Env (like we do with the cancel function).

[reubeno]

Related to #21 ?

[dmcilvaney]

All the even code is brittle when using parallel, but in this case its more that when a log is written it breaks the rendering of a progress bar, and this is especially an issue with parallel workers.