[statsd] add a statsd_timethis context manager
This context manager allows to report to statsd the execution time of any
piece of code, without the need for it to be a function or a method, like::
def some_function():
do_stuff()
with statsd_timethis('some context message'):
do_that()
ensure_this()
^build$
^dist$
\.egg-info$
^.tox$
^.cache$
\.pyc$
\.pyo$
\.bak$
\.old$
\~$
\#.*?\#$
\.swp$
^doc/book/en/apidoc$
\.old$
\.pybuild
cubicweb/server/test/data/slapd.conf
debian/python-cubicweb
debian/*.log
debian/*.substvars
debian/cubicweb-doc
debian/cubicweb
debian/files
syntax: regexp
.*/data.*/database/.*
.*/data/ldapdb/.*
.*/data/uicache/
.*/data/libpython/cubicweb_.*/i18n/.*\.po
^doc/html/
^doc/doctrees/
^doc/book/en/devweb/js_api/
^doc/_build
^doc/js_api/
test-results.xml