This moves and isolates the tar code to tar.c. And the actual
file extraction to disk is moved to extract.c.
A new API is introduced and used for v2 file extraction. This
essentially moves and isolates the apk_sign_ctx_* beast into
extract_v2.c and offers a saner interface to handling packages.
A place holder is added for v3 extraction.
The new v3 applets don't use it, and eventually all applets will
use the new formats only.
This prepares the code for this, and moves trust, id_cache, and
root_fd to apk_ctx which is enough for v3 applets at this time.
The generic code is made to not initialize apk_database if it's
not needed.
This is a flat buffers inspired format that allows fast
mmaped access to the data with low overhead, signature support
and relatively good forward support.
Timo Teräs