Add an image_scale attribute to both Connectors and Cables

It specifies how an image will use any extra space available in its
cell. Allowed values are one of these strings:
- FALSE : keep image its natural size. (Default)
- TRUE : scale image uniformly to fit.
- WIDTH : expand image width to fill.
- HEIGHT : expand image height to fill.
- BOTH : expand both image width and height to fill.

The value is sent to Graphviz as a scale attribute to the <img> tag.
Note that there is normally no extra height in the image cell.

src/wireviz/DataClasses.py

@@ -19,6 +19,7 @@ class Connector:
     subtype: Optional[str] = None
     pincount: Optional[int] = None
     image: Optional[str] = None
+    image_scale: Optional[str] = "FALSE"
     caption: Optional[str] = None
     notes: Optional[str] = None
     pinlabels: List[Any] = field(default_factory=list)
@@ -94,6 +95,7 @@ class Cable:
     wirecount: Optional[int] = None
     shield: bool = False
     image: Optional[str] = None
+    image_scale: Optional[str] = "FALSE"
     caption: Optional[str] = None
     notes: Optional[str] = None
     colors: List[Any] = field(default_factory=list)

src/wireviz/wv_helper.py

@@ -56,7 +56,9 @@ def nested_html_table(rows):
     return html
 
 def html_image(node):
-    return f'''<tdX{' sides="TLR"' if node.caption else ''}><img src="{node.image}"/>''' if node.image else None
+    if not node.image:
+        return None
+    return f'''<tdX{' sides="TLR"' if node.caption else ''}><img scale="{node.image_scale}" src="{node.image}"/>'''
 
 def html_caption(node):
     return f'''<tdX{' sides="LRB"' if node.image else ''}>{html_line_breaks(node.caption)}''' if node.caption else None