Added the enum values unknown to bitmap_format and bitmap_bitdepth
Added code to catch null pimpl in various methods and handle appropriately.
null pimpl occurs when a bitmap has been default constructed is the equivalent of an empty bitmap.
Removed SCL warnings/errors and added some values to the enums.
Update.
Fixed issue, the post-build event was not copying the bitmap.hpp, offending line "..\bitmap_*.hpp"
Added stream manipulators to allow saving and loading as well as some convenience methods for reading/writing bitmaps.

Moved the definitions of the stream operators into new header bitmap_iostream.hpp
New source file to contain the definitions of input/output related code for the libimg::bitmap type
Corrected spelling mistake in _OStreamWriteData
Altered post-build event to use xcopy
Merge branch 'master' of https://github.com/rtlayzell/libimg