Render and sanitize chat messages server-side. (#237)

* Render and sanitize chat messages server-side. Closes #235

* Render content.md server-side and return it in the client config

* Remove showdown from web project

* Update api spec

* Move example user content file

go.mod

@@ -8,7 +8,9 @@ require (
 	github.com/aws/aws-sdk-go v1.34.0
 	github.com/go-ole/go-ole v1.2.4 // indirect
 	github.com/mattn/go-sqlite3 v1.14.0
+	github.com/microcosm-cc/bluemonday v1.0.4
 	github.com/mssola/user_agent v0.5.2
+	github.com/mvdan/xurls v1.1.0 // indirect
 	github.com/nareix/joy5 v0.0.0-20200712071056-a55089207c88
 	github.com/niemeyer/pretty v0.0.0-20200227124842-a10e7caefd8e // indirect
 	github.com/oschwald/geoip2-golang v1.4.0
@@ -16,9 +18,11 @@ require (
 	github.com/shirou/gopsutil v2.20.7+incompatible
 	github.com/sirupsen/logrus v1.6.0
 	github.com/teris-io/shortid v0.0.0-20171029131806-771a37caa5cf
+	github.com/yuin/goldmark v1.2.1
 	golang.org/x/net v0.0.0-20200707034311-ab3426394381
 	golang.org/x/sys v0.0.0-20200808120158-1030fc2bf1d9 // indirect
 	golang.org/x/text v0.3.3 // indirect
 	gopkg.in/check.v1 v1.0.0-20200227125254-8fa46927fb4f // indirect
 	gopkg.in/yaml.v2 v2.3.0
+	mvdan.cc/xurls v1.1.0
 )