QA: Check HTML Correctness & Fix Existing Errors

- _contrib/bco-htmlproof: check HTML for correctness; fail on any errors

- _contrib/bco-htmlproof: accept path for individual page to help debug
  page problems

- (Many files) Convert `&` in numerous elements to `&`

- _templates/download.html: use Liquid filter to automatically escape
  `&` in magnet links.  Also premptively tell HTML not to check the
  magnet link when checking external links (this check is not currently
  enabled)

- _releases/*: Escape `<parameter>` used in multiple Bitcoin Core
  release notes

- _templates/choose-you-wallet.html: change mSigna URL from
  .../coinvault&referer=bitcoin.org to .../coinvault?referer=bitcoin.org

- _templates/community.html: fix duplicate anchors by renaming one
  anchor

- _templates/events.html: move Javascript to separate file because it
  contains forbidden HTML close tags within the `<script></script>`
  tags.

- (Many files, mostly in _translations/) Fix many broken open tags or
  missing close tags.

- _translatios/zh_TW.yml & ko.yml: fix a total of three invalid
  characters (control characters)

_config.yml

@@ -431,7 +431,7 @@ devsearches:
     - "BIP1: BIP purpose and guidelines": "https://github.com/bitcoin/bips/blob/master/bip-0001.mediawiki"
     - "BIP11: m-of-n multisig transactions": "https://github.com/bitcoin/bips/blob/master/bip-0011.mediawiki"
     - "BIP13: P2SH address format": "https://github.com/bitcoin/bips/blob/master/bip-0013.mediawiki"
-    - "BIP14: protocol version & user agent": "https://github.com/bitcoin/bips/blob/master/bip-0014.mediawiki"
+    - "BIP14: protocol version and user agent": "https://github.com/bitcoin/bips/blob/master/bip-0014.mediawiki"
     - "BIP16: pay to script hash (P2SH)": "https://github.com/bitcoin/bips/blob/master/bip-0016.mediawiki"
     - "BIP21: URI scheme": "https://github.com/bitcoin/bips/blob/master/bip-0021.mediawiki"
     - "BIP22: GetBlockTemplate fundamentals": "https://github.com/bitcoin/bips/blob/master/bip-0022.mediawiki"