violate the one definition rule with inconsistent assert enabling.

but not ENABLE_ASSERTS.

there were a lot of samples, causing it to take an excessive amount
of time to converge in some cases.  This fixes it.

column vectors always enabled since violating this is a common user error.

features as a column vector but by reference instead of by value.

with full_object_detection objects in addition to rectangles.

flexible.  This introduces a slight backwards incompatibility in that the
version that loads full_object_detection objects now returns an ignore
rectangle set instead of a parts name list.  But other than that the changes
are backwards compatible with previous version of dlib.

multiple detectors together.

other kernel is specified by the user.

vector represented using a matrix.

begin() and end() methods.

point behavior on different compilers.  In particular, this change avoids having
false "impossible truth box" exceptions being thrown when the object detection
tools are used with the mingw gcc compiler.

prevented the load_image_dataset() routine from working on Windows systems in some
cases.