Rename publicID to base_uri or base_iri

[aucampia]

Base URI is the term used in IETF RFC 3986 Uniform Resource Identifier (URI): Generic Syntax

5.1. Establishing a Base URI

The term "relative" implies that a "base URI" exists against which
the relative reference is applied. Aside from fragment-only
references (Section 4.4), relative references are only usable when a
base URI is known. A base URI must be established by the parser
prior to parsing URI references that might be relative. A base URI
must conform to the syntax rule (Section 4.3). If the
base URI is obtained from a URI reference, then that reference must
be converted to absolute form and stripped of any fragment component
prior to its use as a base URI.