Add Dockerfile support

Original PR by @phyzical
See #266

README.md

@@ -140,6 +140,7 @@ Only a single milestone can be specified. If the milestone does not exist, it wi
 - Clojure
 - Cuda
 - Dart
+- Dockerfile
 - Elixir
 - GDScript
 - Go

syntax.json

@@ -894,5 +894,14 @@
         }
       }
     ]
+  },
+  {
+    "language": "Dockerfile",
+    "markers": [
+      {
+        "type": "line",
+        "pattern": "#"
+      }
+    ]
   }
 ]

tests/test_closed.diff

@@ -564,3 +564,13 @@ index 0000000..d340f6a
 -    * labels: urgent
 -    */
 -}
+diff --git a/src/Dockerfile b/src/Dockerfile
+new file mode 100644
+index 0000000..d340f6a
+--- a/src/Dockerfile
++++ b/src/Dockerfile
+@@ -0,0 +1,4 @@
+-WORKDIR /app
+-ENV PYTHONPATH /app
+-# TODO: Update command
+-CMD ["/app/main.py"]

tests/test_new.diff

@@ -563,6 +563,9 @@ index 0000000..d340f6a
 +    * labels: urgent
 +    */
 +}
+diff --git a/tests/package.move b/tests/package.move
+new file mode 100644
+index 0000000..d340f6a
 --- /dev/null
 +++ b/package.move
 @@ -0,0 +1,20 @@
@@ -586,3 +589,13 @@ index 0000000..d340f6a
 +    * labels: urgent
 +    */
 +}
+diff --git a/src/Dockerfile b/src/Dockerfile
+new file mode 100644
+index 0000000..d340f6a
+--- /dev/null
++++ b/Dockerfile
+@@ -0,0 +1,4 @@
++WORKDIR /app
++ENV PYTHONPATH /app
++# TODO: Update command
++CMD ["/app/main.py"]

tests/test_todo_parser.py

@@ -128,6 +128,9 @@ class NewIssueTest(unittest.TestCase):
     def test_lua_issues(self):
         self.assertEqual(count_issues_for_file_type(self.raw_issues, 'lua'), 2)
 
+    def test_dockerfile_issues(self):
+        self.assertEqual(count_issues_for_file_type(self.raw_issues, 'dockerfile'), 1)
+
 class CustomOptionsTest(unittest.TestCase):
     def setUp(self):
         parser = TodoParser(options={"identifiers":
@@ -304,6 +307,9 @@ class ClosedIssueTest(unittest.TestCase):
     def test_lua_issues(self):
         self.assertEqual(count_issues_for_file_type(self.raw_issues, 'lua'), 2)
 
+    def test_dockerfile_issues(self):
+        self.assertEqual(count_issues_for_file_type(self.raw_issues, 'dockerfile'), 1)
+
 class IgnorePatternTest(unittest.TestCase):
     def test_single_ignore(self):
         os.environ['INPUT_IGNORE'] = '.*\\.java'