feat(cli): add command-line entry point

src/main/kotlin/lumen/cli/Main.kt

@@ -0,0 +1,35 @@
+package lumen.cli
+
+import lumen.Lumen
+import lumen.LumenError
+import lumen.bytecode.Disassembler
+import lumen.formatError
+import lumen.module.ModuleError
+import java.io.File
+import kotlin.system.exitProcess
+
+fun main(args: Array<String>) {
+    if (args.isEmpty()) {
+        Repl().start()
+        return
+    }
+    if (args[0] == "--dump" && args.size > 1) {
+        Disassembler.dump(Lumen.compile(File(args[1]).readText()))
+        return
+    }
+    val path = args[0]
+    val file = File(path)
+    if (!file.exists()) {
+        System.err.println("error: file not found: $path")
+        exitProcess(1)
+    }
+    try {
+        Lumen.runFile(file)
+    } catch (error: ModuleError) {
+        System.err.println(formatError(error.source, error.error))
+        exitProcess(1)
+    } catch (error: LumenError) {
+        System.err.println(formatError(file.readText(), error))
+        exitProcess(1)
+    }
+}