Add initial implementation for running SBT commands.

testing/resources/sbt_hooks_repo/.pre-commit-hooks.yaml

@@ -0,0 +1,6 @@
+-   id: sbt-create-files
+    name: touch
+    entry: touch
+    args: ["file1.txt", "\"file2 with space.txt\""]
+    description: "creates files provided by `args` or `files`"
+    language: sbt

testing/resources/sbt_repo_with_touch_command/build.sbt

@@ -0,0 +1,6 @@
+import TouchCommand._
+
+lazy val root = (project in file("."))
+  .settings(
+    commands ++= Seq(touchCommand)
+  )

testing/resources/sbt_repo_with_touch_command/project/TouchCommand.scala

@@ -0,0 +1,13 @@
+import sbt.Command
+
+import java.nio.file.{Files, Paths}
+
+object TouchCommand {
+  def touchCommand = Command.args("touch", "args") { (state, args) =>
+    args.map(Paths.get(_).toAbsolutePath).foreach { path =>
+      println(f"Creating file: $path")
+      Files.createFile(path)
+    }
+    state
+  }
+}