Binary resources

[michaelhkay]

We have some functions that accept binary input (parse-html, parse-csv) and others that don't (parse-xml, parse-json). There seems to be no obvious justification for the inconsistency.

Related to this:

(a) we have no functions to convert (encode/decode) between binary and string given an encoding

(b) we have no function to read a binary resource from a URI

Both of these are available in the EXPath bin library but should perhaps be promoted to the main spec.