RF: move .bids into .bids/ subpackage and move tests along

This would open for a better structuring of BIDS support code etc.

All bids.utils are imported within bids/__init__.py so there should be
no effect on imports from heudiconv.bids

Author: yarikoptic

heudiconv/bids/__init__.py

@@ -0,0 +1 @@
+from .utils import *

heudiconv/bids/tests/__init__.py

@@ -1,7 +1,7 @@
 """Test functions in heudiconv.bids module.
 """
 
-from heudiconv.bids import (
+from ..utils import (
     maybe_na,
     treat_age,
 )

heudiconv/tests/test_bids.py renamed to heudiconv/bids/tests/test_utils.py

@@ -11,10 +11,10 @@
 from random import sample
 from glob import glob
 
-from .external.pydicom import dcm
+from ..external.pydicom import dcm
 
-from .parser import find_files
-from .utils import (
+from ..parser import find_files
+from ..utils import (
     load_json,
     save_json,
     create_file_if_missing,
@@ -23,7 +23,7 @@
     is_readonly,
     get_datetime,
 )
-from . import __version__
+from .. import __version__
 
 lgr = logging.getLogger(__name__)