All other ranges and slicing uses exclusive end so i think it make sense
to make it consistent.
Update docs and add additional example for non-byte-aligned field.
Also fixes issue showing zero bit ranges as start-NA.
GNU tar docs says:
At the end of the archive file there are two 512-byte blocks filled with binary zeros as an
end-of-file marker. A reasonable system should write such end-of-file marker at the end of
an archive, but must not assume that such a block exists when reading an archive.
In particular GNU tar always issues a warning if it does not encounter it.
Also clean up API usage a bit
