Improve handling of trailing block comments

This is a follow up to r174309 to actually make it work.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@174314 91177308-0d34-0410-b5e6-96231b3b80d8
Add an eachOf matcher.

eachOf gives closure on the forEach and forEachDescendant matchers.
Before, it was impossible to implement a findAll matcher, as matching
the node or any of its descendants was not expressible (since anyOf
only triggers the first match).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@174315 91177308-0d34-0410-b5e6-96231b3b80d8
Implements the convenience matcher findAll.

We found that findAll has been implemented incorrectly multiple times
by various people using the matchers. To prevent further wasted
development effort, it makes sense to add it as convenience matcher
implemented as eachOf(m, forEachDescendant(m)).

This patch also updates the docs with the new matchers.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@174320 91177308-0d34-0410-b5e6-96231b3b80d8