Rather than using a random buffer from stack or heap, and decide
what size to use, create a private memory mapped object...
This simplifies the code in lib/verifysig.c and xbps-create.
With xbps-rindex(8) -c/-r being multithreaded, the memory usage was
insanely high in the build server, with peaks of almost 4GB (this depends
on the file size being processed and number of threads).
Process the file in small chunks instead to compute the SHA256 hash.
The list of required external deps is now confuse, libarchive and openssl.
libxbps now includes a wrapper for proplib prefixed with xbps_ rather than prop_.
These are the core interfaces in the new API:
rpool - Interface to interact with the repository pool.
rindex - Interface to interact with repository indexes.
pkgdb - Interface to interact with local packages.
transaction - Interface to interact with a transaction.
This also brings new repository index format, making the index file
per architecture and being incompatible with previous versions.
The transaction frequency flush option has been removed, and due to
the nature of package states it was causing more harm than good.
More changes coming soon, but the API shall remain stable from now on.
