Default initialization of integer fields

[theoreticalbts]

Currently integer fields aren't initialized in generated code. There are two ways this can be achieved:

• (1) Instead of simple typedef of built-in integer types, integer types in basetypes.hpp should instead be custom types with proper default initializers (and presumably all arithmetic operators).
• (2) Add code generator functionality to the C++ backend to default initialize fields of integer types, or typedefs of integer types.

Approach (2) will probably require extending the basetype declaration syntax to give us a way to tell the codegen "this type has this default initializer".

[sgerbino]

We want to use built in types where ever possible.

[mvandeberg]

Ran in to this bug when implementing #162

I am re-opening in support of the second solution.