Enable PDF output format (port of upstream PR #367)

GraphViz natively supports PDF rendering, so this just adds "pdf" to
the allowed format list and exposes it via the -f P CLI flag.

src/wireviz/wv_cli.py

@@ -19,7 +19,7 @@ format_codes = {
     "g": "gv",
     "h": "html",
     "p": "png",
-    # "P": "pdf",  # TODO: support PDF
+    "P": "pdf",
     "s": "svg",
     "t": "tsv",
 }

src/wireviz/wv_harness.py

@@ -440,7 +440,7 @@ class Harness:
         # graphical output
         graph = self.graph
         for f in fmt:
-            if f in ("png", "svg", "html"):
+            if f in ("png", "svg", "html", "pdf"):
                 if f == "html":  # if HTML format is specified,
                     f = "svg"  # generate SVG for embedding into HTML
                 # SVG file will be renamed/deleted later
@@ -471,10 +471,7 @@ class Harness:
         # HTML output
         if "html" in fmt:
             generate_html_output(filename, bomlist, self.metadata, self.options)
-        # PDF output
-        if "pdf" in fmt:
-            # TODO: implement PDF output
-            print("PDF output is not yet supported")
+        # PDF output is handled by GraphViz in the format loop above
         # delete SVG if not needed
         if "html" in fmt and not "svg" in fmt:
             # SVG file was just needed to generate HTML