Add --dump-markdown flag

Add a new module to handle HTML-to-Markdown conversion and
integrate it into the fetch command via a new CLI flag.

src/Config.zig

@@ -166,6 +166,7 @@ pub const Serve = struct {
 pub const Fetch = struct {
     url: [:0]const u8,
     dump: bool = false,
+    dump_markdown: bool = false,
     common: Common = .{},
     withbase: bool = false,
     strip: dump.Opts.Strip = .{},
@@ -308,6 +309,9 @@ pub fn printUsageAndExit(self: *const Config, success: bool) void {
         \\--dump          Dumps document to stdout.
         \\                Defaults to false.
         \\
+        \\--dump-markdown Dumps document to stdout as Markdown.
+        \\                Defaults to false.
+        \\
         \\--strip_mode    Comma separated list of tag groups to remove from dump
         \\                the dump. e.g. --strip_mode js,css
         \\                  - "js" script and link[as=script, rel=preload]
@@ -410,6 +414,10 @@ fn inferMode(opt: []const u8) ?RunMode {
         return .fetch;
     }
 
+    if (std.mem.eql(u8, opt, "--dump-markdown")) {
+        return .fetch;
+    }
+
     if (std.mem.eql(u8, opt, "--noscript")) {
         return .fetch;
     }
@@ -547,6 +555,7 @@ fn parseFetchArgs(
     args: *std.process.ArgIterator,
 ) !Fetch {
     var fetch_dump: bool = false;
+    var fetch_dump_markdown: bool = false;
     var withbase: bool = false;
     var url: ?[:0]const u8 = null;
     var common: Common = .{};
@@ -558,6 +567,11 @@ fn parseFetchArgs(
             continue;
         }
 
+        if (std.mem.eql(u8, "--dump-markdown", opt)) {
+            fetch_dump_markdown = true;
+            continue;
+        }
+
         if (std.mem.eql(u8, "--noscript", opt)) {
             log.warn(.app, "deprecation warning", .{
                 .feature = "--noscript argument",
@@ -622,6 +636,7 @@ fn parseFetchArgs(
     return .{
         .url = url.?,
         .dump = fetch_dump,
+        .dump_markdown = fetch_dump_markdown,
         .strip = strip,
         .common = common,
         .withbase = withbase,