Add define.hpp to VS project, modify dynamic/static symbol names.

The proposed symbols are used as follows:

Static library build or link: `BC_STATIC`
Dynamic library build: `BC_DLL`
Dynamic library link:

This is the approach taken by most of our dependencies, including ZMQ. It has the advantage of requiring only one (or no) symbol definition in each context, requiring the build to declare itself (static or dynamic), and allowing the consumer to not specify anything unless static linking is required (i.e. works by default).

Also updating some Visual Studio standard project props.