Move metadata handling to per-format file.

[larsbrinkhoff]

There is currently an info.c blob which parses metadata from various file formats. The _info functions should be moved to the appropriate files, and struct pdp10_file should have a new function pointer that refers to those functions. This is currently not trivial because the various _info functions get different parameters.

[larsbrinkhoff]

Actually, why have a separate info function at all? I was thinking the dump tool could just call the read function to build a core image and skip the info function. But now I have dump also pass metadata to the target file so it does need the info call. So it might just as well be done from the read function.

[larsbrinkhoff]

Speaking of metadata, any additional mystery words (see #92) could be regarded as metadata to paste onto the end of the target file.