Formal model of the BIL language and certifying ARMv8 transcompiler

* Dependencies
HOL4 (tested using the git commit: 6a5443a16aa2f5b5c9d4485224aca15d4a40d6be)

* Compilation

- create a symbolic link from l3-machine-code to the proper HOL4 directory
  ln -s <hol_folder>/examples/l3-machine-code l3-machine-code

- compile the BIL model and the transcompiler and the HOL4 heap
  (to speed up loading times)
  cd bin
  <hol_folder>/bin/Holmake

* Translation of a single instruction

  in the ./bin directory prepare a file (e.g. test.sml) with the following
  content

HOL_Interactive.toggle_quietdec();
open HolKernel boolLib bossLib Parse;
open lcsymtacs utilsLib;
open wordsLib blastLib;
open state_transformerTheory updateTheory arm8Theory;
open stateTheory;
open lcsymtacs arm8_stepTheory;
open state_transformerSyntax;
open arm8_stepLib;
open proofTools arithTheory;
open bilTheory arm8bilTheory;
open arm8bilLib;
open arm8stepbilLib;
open arm8bilInstructionLib;
HOL_Interactive.toggle_quietdec();

val th = tc_one_instruction2_by_bin "d37ff800" ``4w:word64`` ``\x.x<+0x100000w:word64``;
print_thm th;

Here, "d37ff800" is the hexadecimal representation of the instruction, ``4`` is
the address where the instruction is stored and ``\x.x<+0x100000w:word64`` is a
property stating where the executable code is stored.

From the ./bin directory execute