Replace skeptic by some custom logic code and rustdoc calls

Unfortunately skeptic pulls all its dependencies in projects using
lettre (see budziq/rust-skeptic#60).

lettre/Cargo.toml

@@ -10,7 +10,6 @@ license = "MIT"
 authors = ["Alexis Mousset <contact@amousset.me>"]
 categories = ["email"]
 keywords = ["email", "smtp", "mailer"]
-build = "build.rs"
 
 [badges]
 travis-ci = { repository = "lettre/lettre" }
@@ -30,10 +29,7 @@ serde_derive = { version = "^1.0", optional = true }
 
 [dev-dependencies]
 env_logger = "^0.5"
-skeptic = "^0.13"
-
-[build-dependencies]
-skeptic = "^0.13"
+glob = "0.2"
 
 [features]
 default = ["file-transport", "crammd5-auth", "smtp-transport", "sendmail-transport"]

lettre/tests/skeptic.rs

@@ -1 +1,57 @@
-include!(concat!(env!("OUT_DIR"), "/skeptic-tests.rs"));
+extern crate glob;
+
+use self::glob::glob;
+use std::env::consts::EXE_EXTENSION;
+use std::env;
+use std::fs;
+use std::path::Path;
+use std::process::Command;
+
+#[test]
+fn test_readme() {
+    let readme = Path::new(file!())
+        .parent().unwrap()
+        .parent().unwrap()
+        .parent().unwrap()
+        .join("README.md");
+
+    skeptic_test(&readme);
+}
+
+#[test]
+fn book_test() {
+    let mut book_path = env::current_dir().unwrap();
+    book_path.push(Path::new(file!())
+        .parent().unwrap()
+        .parent().unwrap()
+        .parent().unwrap()
+        .join("../website/content/sending-messages")); // For some reasons, calling .parent() once more gives us None...
+
+    for md in glob(&format!("{}/*.md", book_path.to_str().unwrap())).unwrap() {
+        skeptic_test(&md.unwrap());
+    }
+}
+
+fn skeptic_test(path: &Path) {
+    let rustdoc = Path::new("rustdoc").with_extension(EXE_EXTENSION);
+    let exe = env::current_exe().unwrap();
+    let depdir = exe.parent().unwrap();
+
+    let mut cmd = Command::new(rustdoc);
+    cmd.args(&["--verbose", "--test"])
+        .arg("-L")
+        .arg(&depdir)
+        .arg(path);
+
+    println!("Running `{:?}`", cmd);
+
+    let result = cmd.spawn()
+        .expect("Failed to spawn process")
+        .wait()
+        .expect("Failed to run process");
+
+    assert!(
+        result.success(),
+        "Failed to run rustdoc tests on README.md!"
+    );
+}