Contributions by @saivann to devel docs

Thanks also (in alphabetical order) to @cbeams, @mikehearn, and
@tgeller, among others.

The last pre-squash commit was: c2b8d562aa107c7b68c60946cea14cdccc5159ad

en/developer-guide.md

@@ -0,0 +1,49 @@
+---
+layout: base
+lang: en
+id: developer-guide
+title: "Developer Guide - Bitcoin"
+---
+
+# Bitcoin Developer Guide
+
+<p class="summary">Find detailed information about the Bitcoin protocol and related specifications.</p>
+
+<div markdown="1" id="toc" class="toc"><div markdown="1">
+
+* Table of contents
+{:toc}
+
+<ul><li><a href="/en/developer-documentation">Return To Overview</a></li></ul>
+
+</div></div>
+
+<div markdown="1" class="toccontent">
+
+<!-- includes should be separated by an empty line to prevent a
+paragraph at the end of one file from breaking the heading at the start
+of the following file. -->
+
+{% include guide_intro.md %}
+
+{% include guide_block_chain.md %}
+
+{% include guide_transactions.md %}
+
+{% include guide_contracts.md %}
+
+{% include guide_wallets.md %}
+
+{% include guide_payment_processing.md %}
+
+{% include guide_operating_modes.md %}
+
+{% include guide_p2p_network.md %}
+
+{% include guide_mining.md %}
+
+{% include references.md %}
+
+</div>
+
+<script>updateToc();</script>