Add support for artist aliases

Use MusicBrainz artist aliases to import files with artist names in an
appriorate locale
fix "import -l logpath" CLI option (GC-518)
update plugin API docs for 1.1
summary paragraph for 1.1b2
fix a couple of typos found by RIT students
remove AutotagError dead code

Another silly mistake identified by the RIT testing team.
Added tag v1.1.0-beta.2 for changeset f28ea9e2ef8d
version bump: 1.1b3
mention GStreamer plugins in BPD docs
docs: may need to create directories
require mutagen >= 1.20

This release fixes several bugs, one of which influences the test cases of
beets (in particular, the MusePack bitrate calculation).
towards filesystem sandboxing of tests

The generic test harness now uses a temporary directory for beets' various
files as well as $HOME. As one packager pointed out, there were various test
failures when $HOME did not exist. This is no longer the case.
tests: remove ad-hoc temporary directories

Now that we have a temporary directory in the shared harness, we can dispense
with the error-prone process of creating them for each test.
test: move DummyIO initialization to harness

This makes it much harder to accidentally leave this I/O isolator installed.
echonest_tempo: sanitize newlines from input

The Echo Nest API confusingly says that the input is missing if it contains a
newline.
echonest_tempo: warn on API error
docs: link to FreeBSD port
fix Sound Check decode (GC-521)

Fixes the case when the gain number is negative.
Sound Check parsing: fix odd-length strings
use gst-python from stock Homebrew