fix logging and crash reports on Windows

"-H=windowsgui" disables stdout on Windows, and the io.Multiwriter used
for logging had stdout as it's first entry, which failed and caused
    logging and line caching to be skipped. stdout is now removed from
    the multiwriter in this situation. Other portion of the issue was
    because crash reports had colons in their names, which Windows
    doesn't like. Fixes #168.

log.go

@@ -27,7 +27,11 @@ func logOutput() (closeFunc func(), err error) {
 			closeFunc = func() {}
 			return
 		}
-		writers = append(writers, colorStripper{f})
+		if PLATFORM == "windows" {
+			writers = []io.Writer{colorStripper{lineCache}, colorStripper{f}}
+		} else {
+			writers = append(writers, colorStripper{f})
+		}
 		closeFunc = func() {
 			w.Close()
 			<-wExit