pre-compile parser objects for performance

[rbuels]

in RequestWorker, at least, I noticed that there are a lot of de-novo constructions of Parser objects. these are expensive, because they compile javascript every time they are created.

could probably get a significant performance boost if these were compiled globally and reused.

[rbuels]

https://github.com/GMOD/cram-js/blob/master/src/cramFile/sectionParsers.js is one not-terribly-clean example of doing this

[cmdcolin]

I went ahead and did this in the requestworker e422584

It could be worth it to have version specific parsers but I haven't had much luck on gathering version information on bigwig files

[cmdcolin]

Close for now, version info following #16

[rbuels]

this probably helps, but i might even take it further and pre-compile them in a module and just export them