Define platform-dependent LibraryHandle type
Start split of PluginVst2x

Linux seems to work fine, other platforms not yet fully migrated.
Rename files to fit convention

Also made a bit more C/C++ friendly.
Update visual studio project files
Fix changed filename
Fix plugin vst 2.x windows features
Finally finish moving the Mac stuff in PluginVst2x
Mac fixes with PluginVst2x split
VST host callback should have C linkage
Linux fixes with PluginVst2x split