First commit towards a linking move_file().
Now reads config['import']['link'], style fix and default setting added.
Style fixes.
Failing to link a file now throws a FilesystemError.
Add support for re-importing added dates.

When re-importing, `item.added` and `album.added` will be preserved if
their path match what they are replacing.
Merge branch 'master' of https://github.com/sampsyo/beets
Should have corrected some of the style checking errors.
Merge branch 'master' of https://github.com/sampsyo/beets
Replace album query with Item.get_album()
artresizer: add check_method()

for the case where we want to know if a specific method is available
add stderr to exception raised by command_output
embedart: add compare_threshold option

if compare_threshold > 0 we call check_art_similarity to return sooner
if it happens that candidate image and embedded one are similar.
embedart: add tests for 'compare_threshold' option

was tricky to write meaningful tests when computing phash of existing 6
pixels image (image-2x3.jpg) so I added new -more representatives-
images.
embedart: docs. explain 'compare_threshold' option
obey Travis orders
reduce image sizes
check_method return method version, add _can_compare()
add can_compare flag to ArtResizer
skip art compare tests if no recent IM version
fix flake8 warnings