Various D2D/DirectWrite/WIC fixes and extensions 

- Memory leak fixes
- Multi-threading extensions 
- Metadata extensions

These changes were made for a customer in the photoprint industry; we use SharpDX on the server side, doing multi-threaded rendering (single factory per thread, using WARP). We fixed a couple of bugs, which we contribute back to the community. We hope these will be integrated into the main repository in one form or another :-)