* Fix copy/paste errors in ls example so file sizes are correctly output.
* BPB updates.
Fix bug in bpb.active_fat(), because active_fat is
only valid when mirroring is disabled.
Add additional santiy checks to BPB deserialization:
1. bytes per sector must be a power of 2
2. 512 <= bytes per sector <= 4096
3. sectors per cluster must be a power of 2
4. 1 <= sectors per cluster <= 128
Also added some comments relating to conditions that
may be useful to WARN about for BPB deserialization:
Z. bpb.reserved_sectors should be 1
Y. bpb.fats should be either 1 or 2
X. bpb.fs_version should be validated as zero
Add syntactic sugar for:
A. bpb.is_fat32()
B. bpb.sectors_per_fat()
C. bpb.total_sectors()
BufStream is universal and can be used with any filesystem so its place is
in different crate. Also moved Partition struct from examples to
fscommon::StreamSlice struct (please note constructor arguments has changed).
Dir methods do not change Dir object itself. They usually clone inner
stream so no change really happens self struct. Underlying partition is
modified but it does not have to affect API. For example see
std::fs::File::set_len. This change greatly simplifies rename API usage.
