Avoid stream polyfill for GFF3/GTF parsing

[cmdcolin]

Fixes GMOD/gff-js#62

I extracted the non-streaming parts of the gff and gtf parsers into their own NPM packages that can be used in isolation, and called the packages gff-nostream and gtf-nostream

This reduces the need for node.js polyfills and the stream-browserify workaround

Potentially, even the streaming parts of @gmod/gff could use gff-nostream as a base package to avoid the code duplication, but right now, this would just remove @gmod/gff and @gmod/gtf entirely from the build in favor of the non-streaming new packages

note: the naming gff-nostream is a little awkward but was hard to come up with something clearly named to distinguish it from @gmod/gff

saves about 50kb ungzipped/15kb gzipped js

[cmdcolin]

The parseStringSync now only return features with no "options" object to be otherwise. reason being

• jbrowse doesn't use comments/sequences/directives
• the other types complicated the typescript (long parseStringSync types in @gmod/gff hints to this)
• not just the typescript but runtime interpretation is challenging with other types because it is just a linear array of "GFF3Item = GFF3Feature | GFF3Directive | GFF3Comment | GFF3Sequence" where there is no stringly typed tag field to really distinguish them easily
• included legacy options like disableDerivesFromReferences

this could be considered to be done somewhat different to add more options, but i think this makes the default behavior best for jbrowse usage