notify: add maxdiffstat option to truncate long file lists
Large scale changes like a new GCC version can easily result in 1MB+
emails due to diffstat alone. The new maxdiffstat option truncates the
list similar to what maxdiff already provides for the diffs.
Differential Revision: https://phab.mercurial-scm.org/D3402
.. 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