Provide an easy way to ignore newlines etc

[dsheets]

RFC 4648 3.1 indicates that some specifications include the insertion of newlines in order to deal with line length limitations in old protocols. Apparently, GitHub's git API blob encoding for base-64 also does this. It would be nice if there were a way to ignore certain characters in base-64 encoded data to avoid this kind of incompatibility. For reference, ocaml-hex does this with an optional ?ignore:char list parameter.

This is the feature equivalent of #5 which simply asks for better, documented exceptions (or a changed return type but compat may preclude that).

[dinosaure]

Related to #51