Remove recursions from computeLiquidity
Rename RippleAsset to Issue and RippleBook to Book:
* Split STAmount out of SerializedTypes.h
* New concept of "Issue consistency": when either both or neither of its
  currency and account are XRP.
* Stop checking for consistency of Issue in its constructor.
* Clarification of mIsNative logic in STAmount.
* Usual cleanups.
Pathfinding Documentation
SHAMap Documentation
Patch Boost to suppress warnings on clang
Add Ledger Entry docs from David's July 3 talk
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.