r_io/r_core-file fixing

Conceptual things:

• in general only code from r_io should be used for io related stuff, io is NOT a core-task
  • wrappers are ok, but no re-implementations (there might be exceptions but those must be reasonable argued)
    • linkage is not argument -> use RIOBind
  • esil-custom reads and writes should use RIOBind too
• if a file gets opened a RIODesc MUST be created
• if a file gets opened in usual cases a RIOMap MUST be created
• if a file gets opened in unsusual cases it's not necessary to create a RIOMap
  • if no RIOMap was created for a fd reading and writing from and to this fd is only possible via r_io_pread and r_io_pwrite
  • this is only an option if only 1 file can be opened for a task or if the fd will never see the user-land
    • Rahash2 for example won't need creating a RIOMap
• if a file gets closed all RIOMaps for that belong to the fd MUST get destroyed
• if a file gets closed the RIODesc MUST get destroyed
• the cores primary task is to delegate the different parts of r2
  • creating a new RIOMap or RIODesc on file-opening is NOT a core-task
  • the same goes for destroying RIOMaps and RIODesc on closing a file
    • there is no need for a map-list in the core directly. core->io->maps is the only list to store maps (for the long run, functions that return a list with maps are ok)

Documentation:

There is no need for a huge documentation!!! But code with fundamental importance often needs a few lines on what it should do, its concept and sometimes a few lines of the code itself need some kind of 'justification' or explanation. libr/io/vio.c is a hardcore example for this RIO-code has fundamental importance, because everything will fail if io does not work correctly. This is needed to make bug-fixing easier, faster and better.

Need review:

libr/io/io.c
libr/core/file.c

Tasks:

• we should fix all the tests before doing this.
  • talk about ioneg
• remove re-implemtations of r_io (middle)
• implement r_io_open_at (easy) ; this should open a file, add a RIODesc and a RIOMap that maps the file to an offset that is passed as an arg
• make r_io_open creating a new map (easy) ; this should open a file, add a RIODesc and a RIOMap that maps the file to 0
  • this means cleaning up r_core_file_open too (hard?)
• implement r_io_open_no_map (easy) ; this should open a file and add a RIODesc. the file can only be accessed via r_io_pread and r_io_pwrite
• make r_io_close destroy all maps that belong to the file that should be closed (easy)
  • this means cleaning up r_core_file_close too (hard?)
• implement (hard); this should find all maps in a certain range, resolve their fds, RIODescs and paddr and then call pwrite
• implement (hard); this should find all sections in a certain range, resolve the maddr that belongs to a vaddr and call mwrite, unsectioned area should be passed directly to mwrite
• implement r_io_reopen (easy); keep the maps for a fd and reopen it, possibly with different permissions
  • this means cleaning up r_core_file_reopen too (hard?)