refactor: add subcommands and separate functionality from artifacts a… (#231)

* refactor: add subcommands and separate functionality from artifacts and images

Signed-off-by: Asra Ali <asraa@google.com>

version/version.go

@@ -0,0 +1,20 @@
+// Copyright 2022 SLSA Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package version
+
+// Version is the version of slsa-verifier.
+// It is meant to be overwritten with
+// -ldflags="-X github.com/slsa-framework/slsa-verifier/version.Version=X.Y".
+var Version = `unknown`