unsqfs: Style changes in read_fs_bytes()

This makes it more consistent with the rest of the refactored code.
unsqfs: Use "c_byte" name consistently

These are a combination of a block size and a compression flag.
Added opkinfo utility

This acts both as an easy way of testing libopk and as example code
for people who would like to use libopk.
unsqfs: Removed additional newlines from TRACE and ERROR macros

The extra newline would help if the terminal contains a partial line,
but chances of that are small. Meanwhile, an error is likely to trigger
multiple error messages from unsqfs since at different levels relevant
context info from that level is printed. Having these lines that belong
to the same error separated by newlines is confusing.
unsqfs: Fixed bug in read_metadata_block()

After reading a block, the input file offset should be increased by
the block's compressed size, not its uncompressed size.

Bug was introduced in commit 54f98302.
unsqfs: Fixed too-strict block size check

Fragment blocks can be smaller than the standard block size and if
the fragment block is compressed there is no way we can know how
large it will be uncompressed before we actually uncompress it.

Bug was introduced in commit af564f19.