Fixes #1188

and find_optimal_rect_filter()

* Problem: integer overflow when calculating sizes (may happen e.g. with very large images)
Solution: change some types from (unsigned) long to size_t

# Conflicts:
#	dlib/dnn/tensor.h

* Fix the fact that std::numeric_limits<unsigned long>::max() isn't always the same number

* Revert serialization changes

* Review fix: use long long instead of size_t

* From long to long long all the way

* Change more types to (hopefully) make the compiler happy

* Change many more types to size_t

* Change even more types to size_t

* Minor type changes

with binaries from a different dlib version.

then take the compiled library file but ignore the config.h file to get a
linker error telling them they have been naughty.  Instead, they should either
use `make install` or `cmake --build . --target install` which will copy the
correct files, or even better, don't install/build dlib as a standalone
library.  Instead, use it the way shown in examples/CMakeLists.txt.

Only define one dlib target in CMake and shared vs. static is determined by BUILD_SHARED_LIBS variable. (#1138)

* Changed cmake so that there is only the dlib target and it isn't forced
to be static or shared, instead, the build type will toggle based on the
state of CMake's BUILD_SHARED_LIBS variable.

* Make CMake build dlib statically whenever DLIB_IN_PROJECT_BUILD==true,
regardless of the state of BUILD_SHARED_LIBS.  This means projects that
use dlib by saying add_subdirectory(dlib) will always statically link to
dlib, unless DLIB_IN_PROJECT_BUILD is explicltly set to false and
BUILD_SHARED_LIBS set to true.

* Change types of tensor's size-related members, so that integer overflow does not happen so easily (see #1148)

* Fix missing typecast

functions.

* Added support for variadic Python functions in find_max_global.

* Add test for find_{min,max}_global on variadic functions.

regardless of the state of BUILD_SHARED_LIBS.  This means projects that
use dlib by saying add_subdirectory(dlib) will always statically link to
dlib, unless DLIB_IN_PROJECT_BUILD is explicltly set to false and
BUILD_SHARED_LIBS set to true.

see what happened.

to be static or shared, instead, the build type will toggle based on the
state of CMake's BUILD_SHARED_LIBS variable.