tests/parsetext.py: add tests for ordinal numbers

HTML documents can represent ordinal numbers in two main ways:

1.  '1st' -- This is the same way as they are represented in plain
    text documents.

2.  '1<sup>st</sup>' -- This takes advantage of HTML layout and
    formatting.

This test case ensures that these two representations have the
same token sequence so that detecting and handling ordinal
numbers is simple and consistent.