repository::cache::file_path() bug fix.
repository::distributor::archiver() implementation.
Repository format update.

Source archive's contents will not be prefixed by source_id.
For example
package/
        index
        src/
            file1
            file2
'file1' and 'file2' will not be prefixed by 'src' in source archive.

repository::distributor::create() was updated.
repository::cache partial implementation.

read_build_snapshot()
read_installation_snapshot()
unpack_source()
unpack_build()
unpack_installation()
pack_build()
pack_installation()