win32: Add gitignore.

Signed-off-by: Ralph Giles <giles@thaumas.net>

win32/.gitignore

+# Visual Studio ignores
+[Dd]ebug/
+[Dd]ebugDLL/
+[Dd]ebugPublic/
+[Rr]elease/
+[Rr]eleaseDLL/
+[Rr]eleases/
+*.manifest
+*.lastbuildstate
+*.lib
+*.log
+*.idb
+*.ipdb
+*.ilk
+*.iobj
+*.obj
+*.opensdf
+*.pdb
+*.sdf
+*.suo
+*.tlog
+*.vcxproj.user
+*.vc.db
+*.vc.opendb