improv: replace eprintln with logger (#18) + fix mod documentation

src/config/config.rs

@@ -34,7 +34,10 @@ impl TryFrom<Ini> for Config {
             match u64::from_str(&exp_time) {
                 Ok(v) => v,
                 Err(e) => {
-                    eprintln!("unable to convert JWT expiration time into u64 err={}", e);
+                    log::error!(
+                        "unable to convert JWT expiration time into u64 details={}",
+                        e
+                    );
                     0
                 }
             }
@@ -59,27 +62,27 @@ impl Config {
     /// validates config ini file
     fn validate(&self) -> bool {
         if self.jwt_exp_time <= 0 {
-            eprintln!("invalid config parameter: JWT expiration time is negative or equals to 0");
+            log::error!("invalid config parameter: JWT expiration time is negative or equals to 0");
             return false;
         }
 
         if self.jwt_issuer == "" {
-            eprintln!("invalid config parameter: JWT issuer is empty");
+            log::error!("invalid config parameter: JWT issuer is empty");
             return false;
         }
 
         if self.jwt_pub_key == "" {
-            eprintln!("invalid config parameter: JWT public key file path is empty");
+            log::error!("invalid config parameter: JWT public key file path is empty");
             return false;
         }
 
         if self.jwt_priv_key == "" {
-            eprintln!("invalid config parameter: JWT private key file path is empty");
+            log::error!("invalid config parameter: JWT private key file path is empty");
             return false;
         }
 
         if self.filestore_path == "" {
-            eprintln!("invalid config parameter: filestore path is empty");
+            log::error!("invalid config parameter: filestore path is empty");
             return false;
         }