name: Add support for ImplicitSha256DigestComponent

This support includes the following new API functions:

- name::Component::isImplicitSha256Digest()
- name::Component::fromImplicitSha256Digest(...)
- Name::appendImplicitSha256Digest(...)
- Updated toUri()/fromUri(...) to support "sha256digest=..." URI
  representation of the ImplicitSha256Digest component

Change-Id: I756c4b94196cf031da98b5689bd60630533dfeb3
Refs: #1640, #2088
data: Enable use of ImplicitSha256Digest component in Data::getFullName

Change-Id: Ib02af6e9c40f447a1b8ab7418fecae82169ceeba
Refs: #1640
interest: Updating Interest::matchesData to use ImplicitSha256DigestComponent

Change-Id: I36660cdacb73efd7f724317b247c8a07578b6fdf
Refs: #1640