YAML: Add support for literal block scalar I/O.

This commit gives the users of the YAML Traits I/O library 
the ability to serialize scalars using the YAML literal block 
scalar notation by allowing them to implement a specialization 
of the `BlockScalarTraits` struct for their custom types.

Reviewers: Duncan P. N. Exon Smith

Differential Revision: http://reviews.llvm.org/D9613


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@237404 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed