Shiro - development build

Unsigned development build of Shiro, from commit 59bf2f3.

Per-user install, no admin prompt. Windows SmartScreen will warn about an
unknown publisher - that is the missing code signature, not a problem with
the download.

Needs an existing Zero-K installation for the engine. Shiro downloads
games and maps itself, including the community content pr-downloader
cannot reach.

Linux packages are built but have never been run by anybody. Reports welcome.