Dynamically sized arrays unimplemented in eWASM target

[egroge]

Dynamically sized arrays are unimplemented for the eWASM target.

At the moment, only fixed size arrays exist. They are stack allocated, and therefore cannot be returned from functions. To implement dynamic arrays, obviously heap allocation will be necessary, which means allocating and freeing memory must be considered. Mallocs and frees can be build with the LLVM wrapper that is in use. Obviously it is essential given the nature of smart contracts that there are no memory leaks when this is implemented.