New ASTMatchers and enhancement to hasOverloadedOperatorName
    
Added two new narrowing matchers:
* hasMethod: aplies a matcher to a CXXRecordDecl's methods until a match is made
  or there are no more methods.
* hasCanonicalType: applies a matcher to a QualType's canonicalType.

Enhanced hasOverloadedOperatorName to work on CXXMethodDecl as well as
CXXOperatorCallExpr.

Updated tests and docs.

Reviewers: klimek, gribozavr


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@176556 91177308-0d34-0410-b5e6-96231b3b80d8