Replace Jekyll highlight tags with fenced code blocks (#1412)

* Replace Jekyll highlight tags with fenced code blocks

Replace Jekyll highlight tags with fenced code blocks.
Canonicalize javascript to js.
Correct highlighting languages.
Add highlighting to code blocks.
Remove leading $ from bash blocks.
Remove empty lines at start and end of code blocks.
Stripped trailing whitespace.

* Fix language of code highlighting

docs/alias.md

@@ -14,7 +14,7 @@ A few notes:
 1. A provider must "opt-in" to supporting ALIAS records. When registering a provider, you specify which capabilities you support. Here is an example of how the
   cloudflare provider declares its support for aliases:
 
-```
+```go
 func init() {
 	providers.RegisterDomainServiceProviderType("CLOUDFLAREAPI", newCloudflare, providers.CanUseAlias)
 }