Add ical test target to detect errors

Add a tox ical test target that calls yaml2ical to check for conflicts
and syntax issues in the meetings directory. This will be used in check
and gate test jobs for the irc-meetings repository.

Change-Id: I7622cfab01031f780274e5488c333db9588ef888

.gitignore

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+.tox
+doc/build
+*.egg-info
+pbr*.egg
+output.ical

test-requirements.txt

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+yaml2ical

tox.ini

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+[tox]
+envlist = ical
+minversion = 1.6
+skipsdist = True
+
+[testenv]
+install_command = pip install -U {opts} {packages}
+setenv = VIRTUAL_ENV={envdir}
+deps = -r{toxinidir}/test-requirements.txt
+
+[testenv:venv]
+commands = {posargs}
+
+[testenv:ical]
+commands = yaml2ical -y meetings -o output.ical -f