fix(destination): Allow the destination to reside in an arbitrary directory

That is to say, the destination will now be interpreted as an entire
  path relative to the source, not simply a filename in the same directory
  as the source.

  Resolves #20.

mkdocs_semiliterate/plugin.py

@@ -401,9 +401,12 @@ semiliterate.ensurelines
         if len(self.patterns) == 0:
             self.patterns = [FlextractionPattern()]
 
-    # Note this needs to be identical to Semiliterate.try_extraction
-    # except with StreamInclusion in place of StreamExtract in the
-    # `extraction =` line, and a couple of options as noted below:
+    # Note that this has diverged noticeably from the
+    # Semiliterate.try_extraction method that it overrides, especially
+    # in regards to adjusting the destination directory.
+    # Hence, great care must be taken when mkdocs-simple-plugin is updated
+    # to make sure that any changes to this method are reflected in the
+    # code below:
     def try_extraction(
             self,
             from_directory,
@@ -418,6 +421,8 @@ semiliterate.ensurelines
         if not to_file:
             return False
         from_file_path = os.path.join(from_directory, from_file)
+        to_file_path = os.path.join(destination_directory, to_file)  # ## ADDED
+        (destination_directory, to_file) = os.path.split(to_file_path)  # ADDED
         try:
             with open(from_file_path) as original_file:
                 utils.log.debug(f"mkdocs-semiliterate: Scanning {from_file}...")