make worker path optional

[jerch]

No description provided.

[jerch]

Postponed, as it is quite involved to get done right (might need some sort of preprocessor logic, which typescript lacks). Also see different build targets in node-sixel.

[jerch]

Also check for obvious perf smells in #1 (comment).

[jerch]

The current worker approach with a distributed ready-to-go worker file furthermore creates some frictions in projects, how to add the worker asset conveniently. Needs some investigations about proper worker file bundling, maybe we can provide an easier to digest asset, which does not collide with package versioning/bundling setups.