XProc steps from standard library in Componize

Several XProc steps implemented in Componize allow standard actions, such as document loading and storing, XSLT processing and XML inclusions.

p:store
Stores a serialized version of its input to a URI, outputs a reference to the location of the stored document.
p:load
Has no inputs but produces as its result an XML resource specified by an IRI.
p:directory-list
Produces a list of the contents of a specified directory.
p:identity
Makes a verbatim copy of the input available on the output.
p:xinclude
Applies XInclude processing to the source document.
p:xslt
Applies an XSLT 1.0 or XSLT 2.0 stylesheet to a document.