Make pybids a conditional import on init

[kaitj]

Closes #88.

Conditionally import pybids in the bids2table.__init__.py if it is available.

[github-actions]

Coverage Report

File	Stmts	Miss	Cover	Missing
__init__.py	9	0	100%
__main__.py	69	8	88%	101, 110, 135, 137–138, 164, 168, 172
_entities.py	112	1	99%	129
_indexing.py	212	5	97%	150, 159–160, 409, 447
_logging.py	31	4	87%	30, 37, 39–40
_metadata.py	48	4	91%	39–40, 66, 71
_pathlib.py	17	3	82%	12–13, 15
_version.py	11	0	100%
pybids
__init__.py	4	0	100%
_bidsfile.py	38	13	65%	71–73, 77–79, 83–85, 89–91, 95
_layout.py	156	45	71%	63, 72, 81, 104, 114–115, 118, 140–141, 156–157, 173–174, 177–181, 186, 188–189, 192–193, 228, 233, 241, 322–324, 389–394, 396, 399–404, 406, 462, 482
_utils.py	13	5	61%	47–50, 52
TOTAL	720	88	87%

Tests	Skipped	Failures	Errors	Time
100	1 💤	0 ❌	0 🔥	16.739s ⏱️