case sensitivity of suffices or other aspects of a file or directory name

[satra]

following up on a more general version of the question about letter-casing of SPIM in PR #881

as far as my brief check went, there is nothing in bids specification that points to case sensitivity of the suffix or more generally about any name. as long as the bids validator or any other tool doesn't care about cases, then this should be fine. if however, the validator checks for case, then perhaps the specification should add a statement about it.

[satra]

also see #956 and #927

[satra]

closing this as #956 covers both components, and has the question about the bids validator supporting this.