Make sure the version number is always up to date

Author: sondr3

Cargo.lock

@@ -23,4 +23,7 @@ fail-on-warnings = []
 git2 = "0.7"
 structopt = "0.2"
 hashbrown = "0.1"
-lazy_static = "1.2"
+lazy_static = "1.2"
+
+[dev-dependencies]
+version-sync = "0.5"

Cargo.toml

@@ -0,0 +1,12 @@
+#[macro_use]
+extern crate version_sync;
+
+#[test]
+fn test_readme_deps() {
+    assert_markdown_deps_updated!("README.md");
+}
+
+#[test]
+fn test_html_root_url() {
+    assert_html_root_url_updated!("src/lib.rs");
+}