cpp: bioformats: Correct exception message in FormatHandler
cpp: bioformats: Document absence of CoreMetadata construction from reader
cpp: bioformats: FormatReader::isUsedFile does not throw boost::filesystem::filesystem_error
cpp: bioformats: CoreMetadata sets bitsPerPixel to 0

This makes it default to the pixel type size, or else it
would be inconsistent.
cpp: bioformats: Add CoreMetadata and Modulo stream operators
cpp: bioformats: Correct used files signatures in FormatReader
cpp: test: Add FormatReader testcase