function objects.  In general, I noted that in most cases they are safe to use
from multiple threads so long as they are not modified.

violation of the strict aliasing rule.  This fixes a bug which caused
find_max_factor_graph_nmplp() to not work properly on some compilers.

asserts when creating a shared library for dlib.

vector_to_matrix(), pointer_to_column_vector(), and pointer_to_matrix() to
mat() (in addition to adding a few more mat() overloads for certain things).

pointer_to_column_vector(), and pointer_to_matrix() methods all into one
convenient interface.  Also made stddev() slightly more general.

This change also deprecates the previous matrix conversion functions.

with incompatible function signatures you got a really confusing error message
from the compiler.  This change makes it so you get a much more informative
error message.