Add version package and update the makefile

The makefile will grab the version info from git and pass it to the
linker so that version information based on tags, commits and commit
times is available in the code.

internal/version/version.go

@@ -0,0 +1,17 @@
+package version
+
+import "fmt"
+
+var (
+	Version        = "dev"
+	GitCommit      = "unknown"
+	CommitDateTime = "unknown"
+	SchemaVersion  = 1
+)
+
+// PrintVersionInfo prints formatted version information to stdout
+func Print() {
+	fmt.Printf("Version:      %s\n", Version)
+	fmt.Printf("Git commit:   %s %s\n", GitCommit, CommitDateTime)
+	fmt.Printf("Schema:       v%d\n", SchemaVersion)
+}