Documenting and testing for deep copying with merging of dicts

Two things happen here:
1. A test is put into place for this situation to show the merge
   with and without a deep copy
2. Documentation is updated to show how to use deepCopy with merging

docs/dicts.md

@@ -83,7 +83,13 @@ Merge two or more dictionaries into one, giving precedence to the dest dictionar
 $newdict := merge $dest $source1 $source2
 ```
 
-This is a deep merge operation.
+This is a deep merge operation but not a deep copy operation. Nested objects that
+are merged are the same instance on both dicts. If you want a deep copy along
+with the merge than use the `deepCopy` function along with merging. For example,
+
+```
+deepCopy $source | merge $dest
+```
 
 ## mergeOverwrite
 
@@ -116,7 +122,13 @@ newdict:
 $newdict := mergeOverwrite $dest $source1 $source2
 ```
 
-This is a deep merge operation.
+This is a deep merge operation but not a deep copy operation. Nested objects that
+are merged are the same instance on both dicts. If you want a deep copy along
+with the merge than use the `deepCopy` function along with merging. For example,
+
+```
+deepCopy $source | mergeOverwrite $dest
+```
 
 ## keys
 

issue_188_test.go

@@ -0,0 +1,33 @@
+package sprig
+
+import (
+	"testing"
+)
+
+func TestIssue188(t *testing.T) {
+	tests := map[string]string{
+
+		// This first test shows two merges and the merge is NOT A DEEP COPY MERGE.
+		// The first merge puts $one on to $target. When the second merge of $two
+		// on to $target the nested dict brought over from $one is changed on
+		// $one as well as $target.
+		`{{- $target := dict -}}
+			{{- $one := dict "foo" (dict "bar" "baz") "qux" true -}}
+			{{- $two := dict "foo" (dict "bar" "baz2") "qux" false -}}
+			{{- mergeOverwrite $target $one | toString | trunc 0 }}{{ $__ := mergeOverwrite $target $two }}{{ $one }}`: "map[foo:map[bar:baz2] qux:true]",
+
+		// This test uses deepCopy on $one to create a deep copy and then merge
+		// that. In this case the merge of $two on to $target does not affect
+		// $one because a deep copy was used for that merge.
+		`{{- $target := dict -}}
+			{{- $one := dict "foo" (dict "bar" "baz") "qux" true -}}
+			{{- $two := dict "foo" (dict "bar" "baz2") "qux" false -}}
+			{{- deepCopy $one | mergeOverwrite $target | toString | trunc 0 }}{{ $__ := mergeOverwrite $target $two }}{{ $one }}`: "map[foo:map[bar:baz] qux:true]",
+	}
+
+	for tpl, expect := range tests {
+		if err := runt(tpl, expect); err != nil {
+			t.Error(err)
+		}
+	}
+}