Add option to strip any BOM from file

[delphidabbler]

Having a byte order mark at the start of a file stored in resources could be problematic, so an option to strip the BOM from text files would be useful.

This would have to be specified on a per file basis with a possible global override.

[delphidabbler]

Since several commands have to affect files on a file by file basis, how we specify this option needs to fit in with those others.

There's a proposal for how to do this here: #1 (comment).

The following format for this command fits in with the proposal.

To determine how to strip BOMs for all files use the -b:strip or -b:keep. The latter is the default, but we need to implement keep for use with individual files.

The following can be added to the file parameters to affect just the file: b:strip or b:keep.

[delphidabbler]

There's an alternative to the structure of per file commands to that mentioned above at later #1 (comment)