Stand alone apt.exe with option for 64bit Osgeo4W

A version of apt that ships with it's own python, so it can be used for Apt From Scratch.

apt.exe - Self contained all in one exe. No installation needed, just run it.

apt-exe-full.exe - A self extracting archive with apt.exe and supporting files. Has faster startup than all-in-one version.

apt-exe-skinny.exe - A self extracting archive with apt.exe and supporting files. It does not include some Microsoft dll's that might be necessary on some machines (#53 for details). Has faster startup than all-in-one version.

This release supports 64bit Osgeo4w! :-)
(see #51 Add 64bit Handling for details and limitations):

set Osgeo4W_root=X:\osgeo-x64
apt --bits=64 setup
apt install shell