Added support for comma seperated queries in querySelectorAll
Added functionality for selecting one level down from parent element
Refactored queryselectorall to make it easier to read and more maintainable
Fixed bug in checkClasses for querySelectorAll, expecting a value where potentially null
Query select function now works recursively for nested children
Refactored select function into smaller functions
Added ability to select with multiple comma separated queries
Implemented next sibling and adjacent sibling selectors