Add tox.ini file * Factor out `commands` for most environments using {envname} substitution to build pytest commande. * Positional arguments are passed on to `pytest` (others may also be passed after a `--`). * Set PATH env variable for tests requiring PostgreSQL. * Also added a `doc` target to build the book. Also update .hgignore exclude .tox directory (where virtualenvs will be created and cubicweb.egg-info created by sdist command). Closes #5447161.

\.svn
^build$
^dist$
\.egg-info$
^.tox$
\.pyc$
\.pyo$
\.bak$
\.old$
\~$
\#.*?\#$
\.swp$
^doc/book/en/apidoc$
\.old$
syntax: regexp
.*/data.*/database/.*\.sqlite
.*/data.*/database/.*\.config
.*/data/database/tmpdb.*
.*/data/ldapdb/.*
^doc/html/
^doc/doctrees/
^doc/book/en/devweb/js_api/
^doc/_build
^doc/js_api/
data/pgdb/
data.*/pgdb.*