Implement C++ version of PRNG.

Using the Mersenne Twister from C++11's standard library a simple C
"library" is created.
Generate JavaScript using Emscripten and pretty print it.

Made sure asm.js is used as target. The intention is to rip out the
resulting asm.js code and prettify it even more to get both a readable and
fast JavaScript PRNG.

Note: emscripten command line with flags
emcc -O2 mt.cpp -s ASM_JS=1 -s DOUBLE_MODE=0 --llvm-lto 1 -s EXPORTED_FUNCTIONS="['_init','_rnd', '_main']" -o mt_proto.js
Prettify generated JavaScript.

Arbitrary chose buffer size (and stack size along with it). Should make
sure to use only as much as really needed. Also, the memcpy shouldn't be
necessary since it should be ok to do the initialisation in place.