add test_lastgenre.py
Move the filtering logic of '_tags_for' function into a dedicated 'filter_tags' function.
lastgenre: add tests functions
wip: rewrite setup_config
get rid of module level options variable

Conflicts:
	beetsplug/lastgenre/__init__.py
lastgenre: rewrite filtering logic to make tests pass

- remove filter_tags() as genres should not be removed this soon while
c14n has not been applied
- group all filtering logic in the function _resolve_genres (formerly
_strings_to_genre)
lastgenre: Restore min_weight option
Use self.config instead of global config
add a test that would fail with the restricted whitelist approach

If no option is set, valid genres should not be rejected. Which is an argument
to have a wide default whitelist.
add a test that would fail with the restricted whitelist approach

If no option is set, valid genres should not be rejected. Which is an argument
to have a wide default whitelist.
Allowing the whitelist to be disabled

By default it is disabled, setting the value to the empty
string will use the built-in whitelist (same behaviour than
c14n).
Canonicalization only return most common genre
Update _setup_config

Give an empty string to obtain default whitelist, None for no whitelist
or a stringlist for a custom one.
Rename/add tests

Rewrite tests now that empty whitelist is allowed.
Merge branch 'KraYmer-lastgenre-tests-new' into lastgenre-tests-new

Conflicts:
	test/test_lastgenre.py
lastgenre: Restore default whitelist
use booleans for whitelist and c14n options

homogenise options setup using booleans, while keeping the empty string
(synonym of ‘true’) for backward compatibility.
Update lastgenre.rst
Isolate lastgenre tests

We now appropriately set up and tear down the fixture for the lastgenre tests.
(This was causing unpredictable failures elsewhere before.)
Use real booleans for whitelist/canonical options

As opposed to the strings "true" and "false".