added section about how to correctly add spec links in tests
Add reference file for flex-flex case

Modify 5 flex-flex cases.
Add reference file for align-item case

Modify 5 align-item  cases.
updated wording per @plinss suggestion
Merge pull request #591 from chenxix/chenxix/csswg-test/flex-align-item

Add reference file for align-item case
Merge pull request #590 from chenxix/chenxix/csswg-test/flex-flex

Add reference file for flex-flex case
Merge pull request #588 from rhauck/speclink-note

added section about how to correctly add spec links in tests
update w3ctestlib