Update path type in Weave TLV specification and code

[jaylogue]

Rename Path to List

For a while now, the TLV Path data type has been used for purposes other than representing strict hierarchical path constructs. For example, the CASE certificate information encoding sends related certificates as a path of certificate elements, allowing for the possibility that they can be tagged in specific ways to indicate their format.

Based on this, it has been decided to rename the Path data type to List, to better reflect prevailing use. Both the code and the Weave TLV Format specification need to be updated to reflect this change.

Relax Tag Requirement

Additionally, #579 has been submitted to relax the requirement that all elements within a List have a tag (i.e. something other than the anonymous tag). This allows Lists to be used in cases where a specific tag isn't required, or the lack of a tag signals a special case. (One example of this is the rdn construct in the Security profile, which uses a list without a tag to signal a multi-attribute X.509 RDN). Once the PR has been merged, the Weave TLV Format specification needs to be updated accordingly.

[jaylogue]

An updated version the Weave TLV Format specification as been submitted in PR #581.