Move/rename indexes and some other files

This makes no difference to how the site is built under Dactyl (other
than where the "Edit Page" links go) but changes the URLs that will
be used for the pages after the migration to Redocly.

In addition to renaming index pages to index.md, I updated the style
guide to reflect the updated conventions, and moved a couple files that
were not in the correct folders for their place in the nav hierarchy.

content/@i18n/ja/references/protocol-reference/serialization.md → content/@i18n/ja/references/protocol/binary-format.md

@@ -13,7 +13,7 @@ curated_anchors:
   - name: タイプリスト
     anchor: "#タイプリスト"
 ---
-# シリアル化フォーマット
+# バイナリフォーマット
 [[ソース]](https://github.com/XRPLF/rippled/blob/develop/src/ripple/protocol/impl/STObject.cpp#L696-L718 "Source")
 
 このページでは、XRP Ledgerのトランザクションとその他のデータの正規バイナリフォーマットについて説明します。このバイナリフォーマットは、トランザクションの内容のデジタル署名を作成および検証するために必要であり、[サーバー間のピアツーピア通信](peer-protocol.html)を含む他の用途にも使用されます。通常、[`rippled` API](http-websocket-apis.html)は、JSONを使用してクライアントアプリケーションと通信します。ただしJSONは、同じデータをさまざまな同等の方法で表現できるため、デジタル署名を付与するトランザクションをシリアル化するのに適したフォーマットではありません。

content/references/protocol-reference/serialization.md → content/references/protocol/binary-format.md

@@ -13,7 +13,7 @@ curated_anchors:
   - name: Type List
     anchor: "#type-list"
 ---
-# Serialization Format
+# Binary Format
 [[Source]](https://github.com/XRPLF/rippled/blob/develop/src/ripple/protocol/impl/STObject.cpp#L696-L718 "Source")
 
 This page describes the XRP Ledger's canonical binary format for transactions and other data. This binary format is necessary to create and verify digital signatures of those transactions' contents, and is also used in other places including in the [peer-to-peer communications between servers](peer-protocol.html). The [`rippled` APIs](http-websocket-apis.html) typically use JSON to communicate with client applications. However, JSON is unsuitable as a format for serializing transactions for being digitally signed, because JSON can represent the same data in many different but equivalent ways.

content/resources/contribute-documentation/contribute-documentation.md → content/resources/contribute-documentation/index.md

@@ -112,9 +112,7 @@ Use the following conventions when creating a page:
 - Don't hard-wrap text in Markdown files.
 - For code samples, try to keep lines no longer than 80 columns wide.
 - When in doubt, follow [Ciro Santilli's Markdown Style Guide (Writability Profile)](https://cirosantilli.com/markdown-style-guide/).
-- Landing pages should be in subfolders and should have the same filename as the folder. For example, the landing page of the "Accounts" page group should be `accounts/accounts.md` with the HTML filename `accounts.html`.
-
-    **Warning:** Don't use `index.md`.
+- The page within a category should be in a subfolder named for that category but can be less verbose (especially if the page title includes words also in the parent directories), should have the filename `index.md`, and a title that is similar to the folder name. For example, the "Protocol Reference" index page is at `references/protocol/index.md`.
 
 - Don't use tab characters for indentation in Markdown or code samples. Use 4 spaces per indent, except in **JavaScript** code samples, which should use 2 spaces per indent.