Change parse() function's arguments`

Input to `parse()` used to be `yaml_input` for the actual YAML, and `file_in` for the YAML file path.
THe latter was only used to resolve relative image paths, not for reading the actual file that was passed.
Therefore, `file_in` was changed to `base_path`; this argument receives the *directory* of the original YAML file, which is more intuitive for the actual use case.

src/wireviz/wireviz.py

@@ -17,12 +17,13 @@
 from wireviz.wv_helper import expand, open_file_read
 
 
-def parse(yaml_input: str, file_in: (str, Path) = None, file_out: (str, Path) = None, return_types: (None, str, Tuple[str]) = None) -> Any:
+def parse(yaml_input: str, base_path: (str, Path) = None, file_out: (str, Path) = None, return_types: (None, str, Tuple[str]) = None) -> Any:
     """
     Parses yaml input string and does the high-level harness conversion
 
     :param yaml_input: a string containing the yaml input data
-    :param file_out:
+    :param base_path: base path used to resolve any relative paths to image files
+    :param file_out: filename of the generated output
     :param return_types: if None, then returns None; if the value is a string, then a
         corresponding data format will be returned; if the value is a tuple of strings,
         then for every valid format in the `return_types` tuple, another return type
@@ -47,7 +48,7 @@ def parse(yaml_input: str, file_in: (str, Path) = None, file_out: (str, Path) =
                         if attribs.get('image'):
                             image_path = attribs['image']['src']
                             if not Path(image_path).is_absolute():  # resolve relative image path
-                                image_path = (Path(file_in).parent / image_path).resolve()
+                                image_path = (Path(base_path) / image_path).resolve()
                                 attribs['image']['src'] = image_path
 
                         if sec == 'connectors':
@@ -210,7 +211,7 @@ def parse_file(yaml_file: str, file_out: (str, Path) = None) -> None:
         file_out = fn
     file_out = os.path.abspath(file_out)
 
-    parse(yaml_input, file_in=Path(yaml_file).resolve(), file_out=file_out)
+    parse(yaml_input, base_path=Path(yaml_file).parent, file_out=file_out)
 
 
 def parse_cmdline():
@@ -252,7 +253,7 @@ def main():
         file_out = args.output_file
     file_out = os.path.abspath(file_out)
 
-    parse(yaml_input, file_in=Path(args.input_file).resolve(), file_out=file_out)
+    parse(yaml_input, base_path=Path(args.input_file).parent, file_out=file_out)
 
 
 if __name__ == '__main__':