cpp: test: xerces tests use ome-test and gtest
cpp: ome-xml: Add ModelException

The Java implementation throws a RuntimeException, which was being
mapped to a C++ std::runtime_error.  This adds a ModelException
class derived from std::runtime_error so it's possible to distinguish
model errors from other generic errors.
xsd-fu: cpp: Make model object arguments more specific
xsd-fu: cpp: Remove todo items

These are items which are either not valid or are not doable.
xsd-fu: cpp: Remove additional todo items
cpp: ome-xml: OMEModelObject compare_element is strictly const
cpp: bioformats: Correct description of UnsupportedCompressionException
cpp: Document detail namespaces
cpp: bioformats: Replace image_size_type with dimension_size_type

image_size_type was redundant since the image indexing is a
combination of the dimensions all using dimension_size_type.
Using dimension_size_type for everything is simpler and more
consistent.
Clean up and add missing tests.
Correct issues brought up by @melissalinkert

See pull request for content. Most substantive change: V3DrawWriter
class now takes endianness of file from metadata and writes the .v3draw
file  with the same byte order as the input.
ITK documentation fixes from @iMichka

See scifio/scifio-imageio#11
Fix Travis build.
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