* improvements to cnn face detection interface

* mmod rectangle object renaming. possibility to set batch size in multi image detection. Added check to make sure images are all the same size.

Added options to input_rgb_image_pyramid that let the user set create_tiled_pyramid()'s padding parameters.

Also changed the default outer border padding from 0 to 11. This effects even
previously trained models.  So any model that doesn't explicitly set the outer
patting to something else will have a padding of 11.  This should be a more
reasonable value for most networks.

of the pyramid image.

output tensor coordinates to use dpoint instead of point.  This way, we can
obtain sub-pixel coordinates if we need them.

better results when run on float and double images.  There was needless
rounding to integers happening in the bilinear interpolation.  Now if you work
with a float image the entire process will run without integer rounding.

* Make noncopyable constructor and destructor default

C++11 provides the functionality.
Defining empty functions cause all classes derived from noncopyable
to be non-trivially constructible and non-trivially destructible.

For example, matrix with compile-time layout by definition does not
require an explicit destructor and should be trivially destructible
; however, deriving from noncopyable makes it non-trivially
destrutible. This also affects vector<T, 2> and vector<T, 3>.

* Delete array2d copy constructor and assignment operators

PNG_LIBRARY set by libpng's FindPNG.cmake does not contain zlib dependancy.  This causes the CHECK_FUNCTION_EXISTS(png_create_read_struct LIBPNG_IS_GOOD) to fail with liner errors, and for dlib to use it's internal copy of PNG.

Updated to use libpng's PNG_LIBRARIES variable.  This also sets both PNG and ZLib libraries in dlib_needed_libraries.