Introduce Module.Context().

This wraps the LLVMGetModuleContext function.
Fix signature of Context.IntType().

This function takes a bit width; it does not return one.
Introduce llvm.ConstNamedStruct().

This wraps the LLVMConstNamedStruct function.
Merge pull request #14 from pcc/modulecontext

Introduce Module.Context().
Merge pull request #15 from pcc/inttype

Fix signature of Context.IntType().
Merge pull request #16 from pcc/constnamedstruct

Introduce llvm.ConstNamedStruct().