feat: add \git escape to double-quoted filenames in inclusion

This allows you to include a file extracted from a specific git commit.
   Still needs documentation.

mkdocs_semiliterate/plugin.py

@@ -16,6 +16,8 @@ from mkdocs_simple_plugin.plugin import SimplePlugin, StreamExtract
 
 import os
 import re
+import subprocess
+import tempfile
 import yaml
 
 
@@ -109,11 +111,21 @@ is checked for `{! ... !}`.
             utils.log.error(errmsg)
             raise EOFError(errmsg)
         filename = body_match['fn']
+        gitextract = False
         if doublequoted:
+            if filename[:5] == r'\git ':
+                gitextract = True
+                filename = filename[5:]
             filename = (filename.encode('latin-1', 'backslashreplace')
                                 .decode('unicode-escape'))
         include_path = self.include_root + '/' + filename
-        print(f"Including |{include_path}|")
+        if gitextract:
+            (write_handle, include_path) = tempfile.mkstemp()
+            utils.log.info(
+                f"semiliterate: extracting {filename} to {include_path}")
+            contents = subprocess.check_output(['git', 'show', filename])
+            os.write(write_handle, contents)
+            os.close(write_handle)
         new_root = re.match(r'(.*)/', include_path)[1]
         try:
             include_parameters = yaml.safe_load(body_match['yml'])