doc/common.txt

mail: use quoted-printable for mime encoding to avoid too long lines (issue3075)

Quoted-printable was already used for the more critical patch mails, so it
should be fine for everything else as well.

.. 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