Adds 3 new amendments (EnforceInvariants, fix1373, FlowCross) to the
Known Amendments table with descriptions for each. (DOC-963)
Adds the new queue parameter to the ledger command (DOC-801) and
reformats some of the surrounding text.
Updates the path specifications page to clarify some rules that relate
to the FlowCross amendment.
The link to the rippled 0.70.0 release tag is expected to fail until
that version is released.
