Supply simple Rizin plugin channeling commands to rz-pm

[XVilka]

Like in Julia language, to look something like:
Rz-pm should have its own REPL mode, which can be entered from the rizin shell by pressing ]. To get back to the rizin shell press backspace or ^C.
It will then change the command prompt:

pkg>

Installing rz-pm should install the rizin plugin, which rizin will automatically load and will provide this command for using directly from the rizin shell.