Some LZMA streams, such as those used in OpenCTM, are encoded without
the unpacked size specified in the header. This is possible to read in
some of the C implementations of LZMA by specifying a header size and
providing the unpacked size as an option to the decoder.

This change adds the same possibility to lzma_rs in a typesafe manner,
where the unpacked size and whether it should be written to the header
is specified explicitly.

Also, make the Options derive Clone and Debug.

These tests do not make sense because they provided a value (None) that
indicated an end marker to be expected in cases where there should be
none.

…for-custom-unpacked-size