Implemented const keyword

src/core/Constant.go

@@ -0,0 +1,13 @@
+package core
+
+import (
+	"git.akyoto.dev/cli/q/src/fs"
+	"git.akyoto.dev/cli/q/src/token"
+)
+
+// Constant registers a single value to be accessible under a descriptive name.
+type Constant struct {
+	Name  string
+	Value token.Token
+	File  *fs.File
+}