Refactor LevelNode

- Lazy level object creation
- Use `getItemsByIntrospection()` to collect BEM items to build
- Unify actualization of blocks and elems in `BundleLevelNode`
merge
Merge branch 'master' into refactor-level-build
Add test to build bundle-elements
Correct sorting in LevelNode.scanLevelItems() and BundleLevelNode.scanLevelItems()
Merge branch 'refactor-level-build'
Add jsdoc for `util.exec()`
Add changelog for 0.5.16
Publish to stable by default
0.5.16
Publish with latest tag
Merge branch 'master' into temp-speed

Conflicts:
	lib/techs/deps.js.js
Update README.ru.md

Обновил ссылки с ветки nodejs
Update README.md

Update links branch nodejs -> master
Merge pull request #256 from banzalik/patch-2

Update paths in README.ru.md
Merge pull request #257 from banzalik/patch-3

Update paths in README.md
BundleNode: Small JSDoc improvements
BundleNode: Change signature of getLevels() method to getLevels(tech)
bem make: Provide a more convenient way to configure the list of bundles and blocks levels to build (close #260)
Merge branch 'master' into temp-speed