Implemented global DOM document cache

* the plan to return XML-nodes from each external function requires a better way to manage the lifetime of many xerces DOM document instances and their support class instances
** this is why DomDocumentCache and DomDocumentCache::item were implemented
** based on std::map so we can easily access the result of old function calls
* changed external read-directory function to return the children of the document node instead of the document node itself
** removes unnecessary cruft in function calls
** will make returning status codes alongside the function result more pleasing to the eye
* updated test transformation to reflect new features

1 files changed, 2 insertions, 1 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 4d50af0..02a9b79 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -18,7 +18,8 @@ add_executable(
 	src/function/read_xml_file.cc
 	src/function/read_directory.cc
 	src/support/filesystem_context.cc
-	src/support/dom_document_guard.cc
+	src/support/dom/document_cache.cc
+	src/support/dom/document_cache_item.cc
 	src/support/xerces_string_guard.cc
 )