Add hasLocalStorage/hasGlobalStorage matchers.

Summary:
Add hasLocalStorage/hasGlobalStorage matchers for VarDecl nodes.
Update the doc. Also add them to the dynamic registry.

Reviewers: klimek

Subscribers: klimek, cfe-commits

Differential Revision: http://reviews.llvm.org/D4034

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@210278 91177308-0d34-0410-b5e6-96231b3b80d8