Fix spelling issues on the Snowplow page

Lots of unescaped variable names here that triggered the spell
checker. Added a few legitimate items to the exceptions list, but
the overwhelming majority of this commit escapes variable names and
marks them (properly) as code.

doc/.vale/gitlab/spelling-exceptions.txt

@@ -203,6 +203,7 @@ http
 https
 idempotence
 idmapper
+Iglu
 inclusivity
 Ingress
 initializer
@@ -372,10 +373,12 @@ pseudonymizer
 Puma
 Python
 Qualys
+Quicktime
 Rackspace
 Raspbian
 Rdoc
 reachability
+Realplayer
 reauthenticate
 reauthenticated
 reauthenticates
@@ -453,6 +456,7 @@ sharding
 shfmt
 Shibboleth
 Sidekiq
+Silverlight
 Sisense
 Sitespeed
 Slack