New file d-typinf.cc
Update dt_t type in D Front End to alias tree_node.
Add new dt_t helper routines to build DECL_INITIAL values.
Implement new TypeInfoDeclaration::toDt routines.
Implement new Type::toDt routines.
Implement new Initializer::toDt routines.
Implement new Expression::toDt routines.
Implement new Declaration::toDt routines.
Implement new Dsymbol::toObjFile routines.
Remove old Symbol data.
Remove Obj::objmod abstraction layer.
Update d_finish_symbol (outdata) to handle new dt_t and send symbols to the back end.
Remove old dt_t functions and dmd backend wrappers.
Remove symbol.h
White space and comment updates.
Clean up StringExp::toDt implementation.