[Feature request] Parallel Updates for EPM?

[iandol]

For my zsh plugin manager zi, parallel update of its packages is ~3-4X faster than serial (around 5secs vs. ~18secs). Currently epm:update is serial. I think it would be much faster if we could optionally use a parallel update (i.e. use run-parallel to run each git pull).

[xiaq]

Parallel updates should be the default.

Some extra work is needed to handle the stdout and stderr of individual update processes though. They can be both captured and only shown when an update fails. At the same time we can probably show some kind of progress indicator.