kick out the jams

Make the module act more like a module. The test code is now an
example. Get rid of redundant "Cmark" prefix in many types. Implement
most of the missing node routines.

examples/render_html.zig

@@ -0,0 +1,42 @@
+const std = @import("std");
+
+const cmark = @import("cmark");
+
+pub fn main() !void {
+    const a = std.heap.page_allocator;
+    const parser = try cmark.Parser.init(&a, .{});
+    defer parser.deinit();
+
+    parser.feed(
+        \\##### Test
+        \\
+        \\This is a test of *commonmark* **parsing**
+        \\
+        \\-----
+        \\
+        \\ * `good`
+        \\   * [bye][@@@]
+        \\
+        \\```
+        \\farewell
+        \\```
+        \\
+        \\[@@@]: greetings (
+        \\    this is a long url title where I can put whatever I want on and on
+        \\    even over many lines
+        \\)
+        \\
+    );
+
+    const node = try parser.finish();
+    defer node.deinit();
+
+    const iterator = try node.iterator();
+    defer iterator.deinit();
+
+    while (iterator.next()) |visit| {
+        std.debug.print("{s} {s}\n", .{ @tagName(visit.event), @tagName(visit.node) });
+    }
+
+    std.debug.print("{s}\n", .{try node.render(.html, .{})});
+}