Shift cache to local appdata on Windows (#260)
Shift cache to local appdata on Windows (#260)

Lektor has been storing its cache in the roaming app data directory
(`%APPDATA%`, typically `C:\Users\username\AppData\Roaming` but quite
possibly on a remote machine, either genuinely living on another machine
or uploaded when you log out and synchronised again when you log in).

For Vista and later, this is not appropriate; the local app data directory
(`%LOCALAPPDATA%`, typically `C:\Users\username\AppData\Local` and defined
as not being on a remote machine) is where it should be instead, because
it is machine-specific (for example, two machines may have different
versions of Python, or different architectures).

APPDATA remains as a fallback before ~, because XP won’t have LOCALAPPDATA
set.
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