Create child/0 type helper

This can help avoid doing too often `[exml:element() | exml:cdata()]` in
specs.

Author: NelsonVides

include/exml.hrl

@@ -11,7 +11,7 @@
 
 -record(xmlel, {name :: binary(),
                 attrs = #{} :: exml:attrs(),
-                children =  [] :: [exml:element() | exml:cdata()]}).
+                children = [] :: [exml:child()]}).
 
 %% Implementation of the exmlAssertEqual/2 macro is a modification of
 %% https://github.com/erszcz/rxml/commit/e8483408663f0bc2af7896e786c1cdea2e86e43d#diff-2cb5d18741df32f4ead70c21fdd221d1

src/exml.erl

@@ -31,6 +31,7 @@
 -export_type([attrs/0,
               cdata/0,
               element/0,
+              child/0,
               item/0]).
 
 -type attrs() :: #{binary() => binary()}.
@@ -44,6 +45,7 @@
 %% </ul>
 -type element() :: #xmlel{}.
 -type item() :: element() | cdata() | exml_stream:start() | exml_stream:stop().
+-type child() :: element() | cdata().
 -type prettify() :: pretty | not_pretty.
 %% Printing indentation rule, see `to_iolist/2'.