explicitly specify the dimensions of the extracted chips.

dimensions.

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.