Add ?sync flag to trigger synchronous compilation

[jhnns]

Originated from pull-request #39

[kisenka]

Any ETA on this?

[jhnns]

Not yet. You could switch isSync to true in your local installation to test it. I heard that sync compilation is awful slow in sufficient complex projects so this has no priority for me.

[jhnns]

Stuck processes should be no issue with 2.0.0 anymore. So this flag is not necessary.