Add README and simplify ViewEngine API

- ViewEngine.init() no longer requires allocator
- render() and renderTpl() accept allocator parameter
- Remove deinit() - no resources to clean up
- Remove unused parse/renderDoc methods
- Add memory management guidance to runtime.zig
- Clean up unused imports and options

src/benchmarks/templates/friends.pug

@@ -0,0 +1,30 @@
+doctype html
+html(lang="en")
+  head
+    meta(charset="UTF-8")
+    title Friends
+  body
+    div.friends
+      each friend in friends
+        div.friend
+          ul
+            li Name: #{friend.name}
+            li Balance: #{friend.balance}
+            li Age: #{friend.age}
+            li Address: #{friend.address}
+            li Image:
+              img(src=friend.picture)
+            li Company: #{friend.company}
+            li Email:
+              a(href=friend.emailHref) #{friend.email}
+            li About: #{friend.about}
+            if friend.tags
+              li Tags:
+                ul
+                  each tag in friend.tags
+                    li #{tag}
+            if friend.friends
+              li Friends:
+                ul
+                  each subFriend in friend.friends
+                    li #{subFriend.name} (#{subFriend.id})