Reorganize the project layout, fix some logging quirks

Signed-off-by: Shin'ya Minazuki <shinyoukai@laidback.moe>

mirai/version.go

@@ -0,0 +1,17 @@
+package mirai
+
+import (
+	"fmt"
+)
+
+var (
+	Revision = "0"
+	Version = "0"
+)
+
+func FullVersion() string {
+	return fmt.Sprintf("%s (r%s)", Version, Revision)
+}
+func PrintVersion() string {
+	return fmt.Sprintf("%s", Version)
+}