doc/common.txt

tests: add a randomized test for pathencode

This is a probabilistic test - it generates different test cases on every
run, unless invoked from the command line with a specific seed.

The default number of tests run should make the tests take about a
second to complete on a semi-modern laptop.

.. 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