fix API to not report own crate version if None given

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "clappconfig"
-version = "0.3.1"
+version = "0.4.0"
 authors = ["Ondřej Hruška <ondra@ondrovo.com>"]
 edition = "2018"
 license = "MIT"

examples/minimal.rs

@@ -30,7 +30,11 @@ impl AppConfig for Config {
 }
 
 fn main() -> anyhow::Result<()> {
-    let cfg = Config::init("Foo Example", "examples/foo.json", None)?;
+    let cfg = Config::init(
+        "Foo Example",
+        "examples/foo.json",
+        env!("CARGO_PKG_VERSION"),
+    )?;
 
     trace!("Trace message");
     debug!("Debug message");

examples/rotn.rs

@@ -149,7 +149,7 @@ fn main() -> anyhow::Result<()> {
         env!("CARGO_PKG_AUTHORS")
     );
 
-    let main = Config::init("Rot-N", "rotn_config.json", Some(&version))?;
+    let main = Config::init("Rot-N", "rotn_config.json", &version)?;
 
     // rot13
 

src/lib.rs

@@ -62,8 +62,9 @@ pub trait AppConfig: Sized + Serialize + DeserializeOwned + Debug + Default {
     fn configure<'a>(self, _clap: &clap::ArgMatches<'a>) -> anyhow::Result<Self::Init>;
 
     /// Initialize the app
-    fn init(name: &str, cfg_file_name: &str, version: Option<&str>) -> anyhow::Result<Self::Init> {
+    ///
-        let version = version.unwrap_or_else(|| env!("CARGO_PKG_VERSION"));
+    /// Use `env!("CARGO_PKG_VERSION")` to get a version string from Cargo.toml
+    fn init(name: &str, cfg_file_name: &str, version: &str) -> anyhow::Result<Self::Init> {
         let clap = clap::App::new(name)
             .arg(
                 clap::Arg::with_name("config")