setup.py: Provide instructions to install cmake

If cmake_path is not found, either cmake is not installed
or cmake is not in the PATH. Hence, we also give instructions
on how to install cmake if the path is not found.

of the parameter vectors.

save_jpeg: Use TRUE instead of true

In some verisons on jpeg, TRUE is an enum, and so `true`
fails because it is not of the enum's type. Now, all the
libjpeg calls use TRUE/FALSE.

Fixes https://github.com/davisking/dlib/issues/129

learning rate.

shenanigans in a separate process.

just dlib exceptions.

Concat layer

Added getter for trainer::train_one_step_calls

dimensions of its inputs rather than always outputting a tensor that has the
dimensions of its immediate predecessors.