Add documentation for ledger entries
Impose a local limit on path lengths
Find 'sabfd' paths
This permits USD/GW1 to be bridged to USD/GW2 by BTC/GW3 or
USD/GW1 to be bridged to BTC/GW2 by CNY/GW3. See RIPD-335.
account_tx resume bugfix
Various tidying:
* Fix unused variable warnings.
* Clean unused items from TER.
* Improvement to LES use of shared_ptr.