Expand libtinycode

* Support loading of multiple libtinycodes
  * Implement `ptc_load` which returns an object working as the
    libtinycode's interface.
  * Various other improvements and new functions in the libtincode
    interface
* CPU intialization
  * Automatically choose a CPU depending on the current architecture
  * Implement `initialize_cpu_state` which performs all the
    architecture-specific initialization steps
* `mmap` memory areas before translation
  Feed into libtinycode the code and the corresponding address ranges,
  so it can mmap it and avoid translating code outside of these regions.
* Implement `ptc_disassemble`
* Implement some dummy functions needed by the i386 backend
* Various other aesthetic changes
* Make `tb_link_page` non-static
* Let `ptc_instruction_*` functions take a pointer to `PTCInterface` to
  be able to perform sanity checks