doc/common.txt

formatter: improve implementation of data method

This alternate syntax was proposed by Bryan O'Sullivan in a review of
772b3764d3e8.  I haven't been able to measure any particular performance
difference, but the new syntax is more concise and easier to read.

.. Common link and substitution definitions.

.. |hg(1)| replace:: **hg**\ (1)
.. _hg(1): hg.1.html
.. |hgrc(5)| replace:: **hgrc**\ (5)
.. _hgrc(5): hgrc.5.html
.. |hgignore(5)| replace:: **hgignore**\ (5)
.. _hgignore(5): hgignore.5.html