Statically link std libraries under mingw

Allows for easier redistribution.

No functional change.
Use DD-MM-YY as date format

In engine name and version number.

No functional change.
Convert Readme to markdown format

Looks better on GitHub, that supports this format.

No functional change.
Avoid a tricky line in shelter_storm()

kf = (kf == FILE_A) ? kf++ : ....

is tricky becuase kf is updated twice and it happens
to do the right thing just by accident.

Rewrite in a better way.

Spotted by pdimov

No functional change.