* Renamed the macro for exporting symbols to IECORE_API, which switches between IECORE_EXPORT/IECORE_IMPORT from the IECORE_EXPORTS define.

* Added includes to headers so that MSVC recognises forward-declaration of other classes (solves issues with intrusive_ptr.h in MSVC with RefCounted sub-classes).

* The exporting header is now called IECore/Export.h