Implement deprecated attribute for msvc12.
Make implicit casts explicit, eliminate msvc warnings.
Fix msvc compile error on base58 unit test.
Change to compiler (vs. Windows) test for export defines.
Avoid casting int to bool in c++.
Add ec_keys.hpp/cpp to VS project.
Update NuGet dependencies for updated EC.
Merge pull request #9 from evoskuil/develop

Implement deprecated (msvc), fix test (msvc), explicit casts, EC updates.