Hello World plus minor change

Essentially, this pull requests adds a Hello World example (working on my machine). What is a new programming language without a hello world example?

The code simply prints Hello World on screen. The code is quite long to make fun with the language, and to avoid a very repetitive supercazzola to print out one char at a time.

There is as well some minor changes to the code: I have converted integer/float conversion from c++11 to older code, as we cannot suppose the availability of a newer compiler.