Add test cases for new extra

Author: Crozzers

test/tm-cases/markdown_file_links.html

@@ -0,0 +1,3 @@
+<p><a href="./file.html">This is a link to a markdown file</a></p>
+
+<p><a href="./something.html">This is a reference to a markdown file link</a></p>

test/tm-cases/markdown_file_links.opts

@@ -0,0 +1 @@
+{'extras': ['markdown-file-links']}

test/tm-cases/markdown_file_links.text

@@ -0,0 +1,6 @@
+[This is a link to a markdown file](./file.md)
+
+[This is a reference to a markdown file link][]
+
+
+[This is a reference to a markdown file link]: ./something.md

test/tm-cases/markdown_file_links_no_linkdefs.html

@@ -0,0 +1 @@
+<p><a href="./something.md">This is a reference to a markdown file link</a> but link definition swapping is disabled</p>

test/tm-cases/markdown_file_links_no_linkdefs.opts

@@ -0,0 +1 @@
+{'extras': {'markdown-file-links': {'link_defs': False}}}

test/tm-cases/markdown_file_links_no_linkdefs.text

@@ -0,0 +1,4 @@
+[This is a reference to a markdown file link][] but link definition swapping is disabled
+
+
+[This is a reference to a markdown file link]: ./something.md