Annotate connectives in xrefs

[opoudjis]

Crossreferences autogenerate with internationalisation connectives and nesting of cross-reference text:

<xref target="note1"><location target="note1" connective="and"/><location target="note2" connective="and"/></xref>

can end up rendered as:

 <xref target="note1">Clause 2.1, Note 1</xref> and <xref target="note2">Clause 2.2, Note 1</xref>
      Clause 2.2, <xref target="note2">Note 1</xref> and <xref target="note3">Note 2</xref>

As we are semantically annotating cross-reference text out of #617, it would make sense to annotation the inserted "and" and "," in the foregoing, as spans of class fmt-xref-connective. Doing so would involve updating isodoc-i18n, since it is internationalised, so I will delay it.

[opoudjis]

Bringing this forward, since it's just going to make rewriting test cases quicker to do it now.

[opoudjis]

The syntax of i18n connective templates is:

%1, %2
%1, and %2
%1の%2

It will become:

%1<conn>, </conn>%2
%1<conn>, and</conn>%2
%1<conn>の</conn>%2

It will be the responsibility of the caller to replace <conn>,</conn> with appropriate markup; in our case, <span class='fmt-connective'>, </span>

Adding <enum-comma></enum-comma> for "a, b, and c", and <comma></comma> for "Clause 1, Table 2".