Added section on running a developed extension

Also some typos and updates.
Fixed typo in comment
avahi: Service hostname must contain, resolvable fqdn with .local appended to it.
Merge pull request #795 from dz0ny/fix/mdns_resolve

avahi: Service hostname must contain, resolvable fqdn
docs: Update changelog wrt PR #795
Update .mailmap
Fix mopidy/audio/scan.py to avoid negative values in track lengths

The fix is the most elegant I found, but it might pass undetected.
Fix the Line too long lint error
Merge pull request #796 from ifosch/gh662

Fix negative track lengths on radio streams. Fixes #662.
docs: Update changelog
Workaround for RasPi selecting jack server.
Fixed long line Flake8 warning.
Test with multiple versions of tornado. See #798
Merge pull request #806 from dz0ny/tornado_matrix

Test with multiple versions of tornado.
tox: Fix Tornado version mismatch in env name and deps

(cherry picked from commit acef38a6c75bb46324d4a49b57552f2320f02694)
travis: Update tox env names

(cherry picked from commit e950cf5501bf82787e202024774a4e5f6f85ed27)
Merge pull request #801 from arjunrn/develop
audio: Link to context of why we demote jack sinks
(cherry picked from commit 29019d94af42e81b478dd283a70c809f78e5f650)
doc: Add changelog entry for jack sink fix
(cherry picked from commit 0440703abbe8a96eb45a1795fdca2482f7998b9d)

Conflicts:
	docs/changelog.rst
docs: Update authors

(cherry picked from commit 614dc93ad85e58be563f3cb7cfb4ffa3c951b202)