esm bundle, multiple graphs per subject, autolinking

This release adds an esm bundle (dist/oldm.mjs) that includes N3 and JSONTag.
It also keeps track of the source graphs for each subject, it doesn't yet allow you to add predicates to the source graphs later. So no option to update the source files yet. If a subject has triples in multiple graphs, the resulting object merges those triples into a single subject.
The separator character is now configurable, default is still $.