rpmlib: RPM reader API

[tony-iqlusion]

This issue tracks the ability to read RPM package files. Presently no support is available.

Some reference information on the API is available here, courtesy the Fedora RPM Guide:

• C API: TBD
• Python API: https://docs.fedoraproject.org/ro/Fedora_Draft_Documentation/0.1/html/RPM_Guide/ch16s04.html

#11 is fixed, and #19 added transaction set support, so this is ready to work on for any interested takers.

[n3npq]

The easiest bindings are rpmInstall() and rpmErase() in lib/rpminstall.c, copying rust args into the needed structure. There are also similar interfaces for query/verify/sign available. All the tables for popt option processing are available for needed flags if you also bind libpopt.

If you want a lower level interface, use rpmReadPackageFile() which verifies package signatures.

I would avoid doing similar to Python interfaces which were mis-designed to accomodate "I don't want to verify signatures! I don't want to use a transaction!" politics from a long time ago.