add bytecode compiler and vm

[matsud224]

This pull-request adds a bytecode compiler and a virtual machine.
SATySFi interpreter is slow(see #63). This bytecode compiler improves an evaluation performance.
For example, it takes about 90 minutes to make a pdf of pi on my laptop by
the interpreter. By using the bytecode compiler, it only takes about 4 minutes.
The bytecode compiler can coexist with interpreter. You can use it by adding --bytecomp command line option.

To build the virtual machine, a Ruby script 'gen_code.rb' is used. This script reads 'src/frontend/bytecomp/vminstdef.yaml' and generates OCaml codes.
'vminstdef.yaml' is written in YAML format and contains instruction & primitive definitions. This mechanism makes it easier to add a new VM instruction or primtive. But now, interpreter and virtual machine are not share the code. Therefore you have to update both an interpreter and a virtual machine if you modify evaluator or add a new primitive.

[gfngfn]

Thank you so much for sending a really amazing PR! I confirmed that the compiler and the VM work fine. I merged the PR after making the interpreter and the VM share some duplicate code and the definition of primitive operations.