Added a basic build mecanism.

Simply add the file to compile into the _CoqProject file and run build.sh.
The produced Makefile has the usual targets (all, html, ...) corresponding
to the project specification.
Merge branch 'build' into integration
Added the Coq representation of ML integers.

ML integers (int) are mapped from Z binary numbers. Obviously, this
mapping is incorrect but it should be sufficient for the compilation
purpose.
Added the [int] syntactic sugar.
Added the src/mltypes/int.v file to targets.
Merge branch 'integer' into integration