add command line parameter to print the version

The version is defined in build.zig. We use git describe to the
the build version. For release versions we enforce that the version
in build.zig and build.zig.zon must be equal to the output of
git describe.

build.zig.zon

@@ -2,7 +2,7 @@
     .name = "zig-totp",
     // This is a [Semantic Version](https://semver.org/).
     // In a future version of Zig it will be used for package deduplication.
-    .version = "0.0.0",
+    .version = "0.1.0-dev",
 
     // This field is optional.
     // This is currently advisory only; Zig does not yet do anything