feat: Allow '.md' extension

This makes it easier for text editors and github to format the files for
human reading / editing.

In doing this, we need to gracefully handle unrelated `.md` files.  This
means we allow, rather than error, if there are no test cases.
We don't want syntax mistakes to cause tests to be silently ignored, so
we elevate these cases as `ignored` in the UI.

Author: epage

examples/README.md

@@ -0,0 +1 @@
+Examples and example test cases

examples/example-fixture.trycmd renamed to examples/example-fixture.md

@@ -146,6 +146,12 @@ impl Case {
             }
         };
 
+        if sequence.steps.is_empty() {
+            let output = Output::sequence(self.path.clone());
+            assert_eq!(output.spawn.status, SpawnStatus::Skipped);
+            return vec![Ok(output)];
+        }
+
         let fs_context = match crate::FilesystemContext::new(
             &self.path,
             sequence.fs.base.as_deref(),

src/runner.rs

@@ -46,7 +46,7 @@ impl TryCmd {
                 sequence.steps[0].expected_stderr = stderr;
 
                 sequence
-            } else if ext == std::ffi::OsStr::new("trycmd") {
+            } else if ext == std::ffi::OsStr::new("trycmd") || ext == std::ffi::OsStr::new("md") {
                 let raw = crate::File::read_from(path, false)?.into_utf8().unwrap();
                 Self::parse_trycmd(&raw)?
             } else {
@@ -190,10 +190,6 @@ impl TryCmd {
             }
         }
 
-        if steps.is_empty() {
-            return Err("No runs in trycmd file".into());
-        }
-
         Ok(Self {
             steps,
             ..Default::default()

src/schema.rs

@@ -3,5 +3,5 @@
 fn example_tests() {
     let t = trycmd::TestCases::new();
     t.register_bins(trycmd::cargo::compile_examples([]).unwrap());
-    t.case("examples/*.trycmd");
+    t.case("examples/*.md");
 }