Rewrite metadata syntax documentation

Rewrite it as reStructuredText so that it can be hosted alongside the
API documentation on Read The Docs, which allows linking to WIP syntax
documentation.

scripts/appveyor/deploy_docs.ps1

@@ -13,7 +13,6 @@ $replaceSelect = '$1' + "`n" + '    <option value="' + $env:APPVEYOR_REPO_TAG_NA
 $docsFiles = @(
   'images'
   'licenses'
-  'LOOT Metadata Syntax.html'
   'LOOT Readme.html'
 )
 

scripts/archive.js

@@ -152,7 +152,6 @@ function createAppArchive(rootPath, releasePath, tempPath, destPath) {
   [
     'images',
     'licenses',
-    'LOOT Metadata Syntax.html',
     'LOOT Readme.html',
   ].forEach((item) => {
     fs.copySync(

scripts/installer.iss

@@ -102,8 +102,6 @@ DestDir: "{app}"; Flags: ignoreversion
 Source: "{#buildir}\Release\resources\l10n\en-US.pak"; \
 DestDir: "{app}\resources\l10n"; Flags: ignoreversion
 
-Source: "docs\LOOT Metadata Syntax.html"; \
-DestDir: "{app}\docs"; Flags: ignoreversion
 Source: "docs\LOOT Readme.html"; \
 DestDir: "{app}\docs"; Flags: ignoreversion isreadme
 Source: "docs\licenses\*"; \