Improvements to typings

[megoth]

This is an issue where I'll note improvements that can be done to various typings.

• [x] graph(features, opts) -> graph(features = [], opts = {}): Allows creation of with simply const store = graph()
• [x] Fetcher.delete(uri, options) -> Fetcher.delete(uri, options = {}): Don't need to supply options all the time
• [x] Store.add should allow string as third parameter (object, i.e. it should be interpreted as a Literal)
• [x] Make sure that exported types from methods (e.g. type NamedNode for methods such as namedNode and sym) are compatible with methods that have parameters that reflect these types.
  • namedNode
  • st
  • Store.any
  • Store.canon
  • Store.each
  • Store.statementsMatching
  • sym
• [x] The returned type of Fetcher.load should be dependent on the type of the first parameter: If its an array, return an array of promises, if its a singular value, return a single promise
• [x] UpdateManager.editable(docUri, kb) -> UpdateManager.editable(docUri, kb?) so that you don't have to supply kb

Probably more to come, I'll update this as I find them - propose that the one that fixes this strikes out the issues as they are fixed

[joepio]

Work in progress branch: https://github.com/linkeddata/rdflib.js/tree/typing-improvements-%23376

[timbl]

In general I prefer Store.add() to take anything anywhere to be safe. In N3 you can put a literal as the subject, bnodes as predicate, etc ... best to be liberal.