modify project structure

to better follow modern convention and good practices

tests/test_generate.py

@@ -0,0 +1,23 @@
+from gmirator.generate import (
+    process_file,
+    process_list,
+    process_inline,
+    repl_url,
+    repl_heading
+)
+
+
+def test_process_file():
+    pass
+
+def test_process_list():
+    pass
+
+def test_process_inline():
+    assert process_inline("*Hello* ~~world~~!") == "<em>Hello</em> <s>world</s>!"
+
+def test_repl_url():
+    pass
+
+def test_repl_heading():
+    pass