Dev Docs (Formatting Only): Convert Fake Subheadings To Real Subheadings

Converts fake subheadings created using **bold** to real HTML
subheadings without adding them to the table of contents.

Also fixes a link broken by commit 4e067ac89e74b and adds a Makefile
test to catch future similar breakage.
Ignore .no_toc titles when selecting active toc entry
Allow links in anchor affordance titles
Merge remote-tracking branches 'saivann/notoc' and 'saivann/notocanchor' into notoc
Dev Docs: Revise Makefile Test To Check For Auto Links In Subheadings
Drop unused translations
Merge branch 'notoc' (Pull #661: Convert Fake Subheadings To Real Subheadings)
Dev Docs: Document Headers-First (And, By Extension, Blocks-First)

This commit provides a detailed overview of 0.10's headers-first block
download method and significantly improves our current documentation of
the current block download method, which I've called retroactively named
blocks-first for parallelism.

New And Significantly Revised:

* New Initial Block Download (IBD) section (h3) with separate
  Blocks-First and Headers-First subsections (h4) using parallel
  composition.

* 100% rewritten Blocks Broadcasting subsection describing in
  blocks-first relay in much more detail, plus new descriptions of
  headers-first relay and SPV downloading.

* New Orphan Block subsection (under Blocks Broadcasting) describing
  orphan blocks and how they're handled differently under blocks-first
  and headers-first. Also includes a simple illustration of the
  difference between orphan blocks and stale blocks. Thanks to @luke-jr
  for his s/orphan block/stale block/ commit a couple months ago---that
  made this commit much easier.

Edits:

* Cleaned up a couple cases missed by previous s/orphan/stale/ commit
  because they used past tense (orphaned).

* Mentioned direct RPC changes introduced by headers-first pull in the
  RPC docs. TODO'd those sections to ensure we provide updated examples
  once 0.10 is released.

* In P2P reference section, mentioned that a `block` message can be sent
  unsolicited by miners.

* Mention that `getheaders` and `headers` were added in protocol
  version 31800.

* Moved a few internal links around and added a few new internal links.

Administrivia:

* Started adding "TODOv0.10" in HTML comments to places that need to be
  updated when 0.10 is released so that I can easily git grep for that
  tag later.