Moved docgen out of the sdk into pkg/

sdk/lib/_internal/docgen/lib/dart2yaml.dart

-/**
- * This library is used to convert data from a map to a YAML string.
- */
-library dart2yaml;
-
-/**
- * Gets a String representing the input Map in YAML format.
- */
-String getYamlString(Map documentData) {
-  StringBuffer yaml = new StringBuffer();
-  _addLevel(yaml, documentData, 0);
-  return yaml.toString();
-}
-
-/**
- * This recursive function adds to its input StringBuffer and builds
- * a YAML string from the input Map.
- */
-// TODO(tmandel): Fix quotes with String objects.
-void _addLevel(StringBuffer yaml, Map documentData, int level) {
-  documentData.keys.forEach( (key) {
-    _calcSpaces(level, yaml);
-    yaml.write("\"$key\" : ");
-
-    if (documentData[key] is Map) {
-      yaml.write("\n");
-      _addLevel(yaml, documentData[key], level + 1);
-
-    } else if (documentData[key] is List) {
-      var elements = documentData[key];
-      yaml.write("\n");
-      elements.forEach( (element) {
-        if (element is Map) {
-          _addLevel(yaml, element, level + 1);
-        } else {
-          _calcSpaces(level + 1, yaml);
-          yaml.write("- ${_processElement(element)}");
-        }
-      });
-      
-    } else {
-      yaml.write(_processElement(documentData[key]));
-    }
-  });
-}
-
-/**
- * Returns an escaped String form of the inputted element.
- */
-String _processElement(var element) {
-  return "\"${element.toString().replaceAll("\"", "\\\"")}\"\n";
-}
-
-/**
- * Based on the depth in the file, this function returns the correct spacing
- * for an element in the YAML output.
- */
-void _calcSpaces(int spaceLevel, StringBuffer yaml) {
-  for (int i = 0; i < spaceLevel; i++) {
-    yaml.write("  ");
-  }
-}