tpl: Add reflect namespace

Add a reflect namespace that offers a two boolean functions for
testing if a value is a map or slice.

Fixes #4081

docs/content/en/functions/reflect.IsMap.md

@@ -0,0 +1,25 @@
+---
+title: reflect.IsMap
+description: Reports if a value is a map.
+godocref:
+date: 2018-11-28
+publishdate: 2018-11-28
+lastmod: 2018-11-28
+categories: [functions]
+menu:
+  docs:
+    parent: "functions"
+keywords: [reflect, reflection, kind]
+signature: ["reflect.IsMap INPUT"]
+workson: []
+hugoversion: "v0.53"
+relatedfuncs: [reflect.IsSlice]
+deprecated: false
+---
+
+`reflect.IsMap` reports if `VALUE` is a map.  Returns a boolean.
+
+```
+{{ reflect.IsMap (dict "key" "value") }} → true
+{{ reflect.IsMap "yo" }} → false
+```

docs/content/en/functions/reflect.IsSlice.md

@@ -0,0 +1,25 @@
+---
+title: reflect.IsSlice
+description: Reports if a value is a slice.
+godocref:
+date: 2018-11-28
+publishdate: 2018-11-28
+lastmod: 2018-11-28
+categories: [functions]
+menu:
+  docs:
+    parent: "functions"
+keywords: [reflect, reflection, kind]
+signature: ["reflect.IsSlice INPUT"]
+workson: []
+hugoversion: "0.53"
+relatedfuncs: [reflect.IsMap]
+deprecated: false
+---
+
+`reflect.IsSlice` reports if `VALUE` is a slice.  Returns a boolean.
+
+```
+{{ reflect.IsSlice (slice 1 2 3) }} → true
+{{ reflect.IsSlice "yo" }} → false
+```