Fix subscribing to "real time" transactions.
Fix a pathfinding bug
Fix a compiler warning in Ledger::visitStateItems
General refactoring, using C++11
* Remove broken RecycledObjectPool

* Fix beast::ServiceQueue using List instead of LockFreeStack

* Add class semaphore, fixes broken Semaphore

* Move crytpo module files to new beast directory

* Use c++11 replacements for boost and beast types:
  - std::atomic instead of beast::Atomic
  - std::function instead of boost::function, beast::function
  - std::unique_ptr instead of beast::ScopedPointer
  - std::shared_ptr instead of boost::shared_ptr

* Remove modules:
  - beast_db
  - beast_crypto
  - beast_extras

* Remove unnecessary classes:
  - AbstractFifo
  - AddConst
  - AtomicCounter
  - AtomicFlag
  - AtomicPointer
  - AtomicState
  - CopyConst
  - Expression
  - ForwardList
  - IfCond
  - Interval
  - IntrusiveArray
  - KeyvaDB
  - PointerToOther
  - PointerTraits
  - RemoveConst
  - RemoveConstVolatile
  - RemoveReference
  - RemoveVolatile
  - SharedObjectArray
  - SingleThreadedSharedObject
  - SophiaDB factory
  - SortedSet
  - WeakReference
  - beast::unique_ptr
Pathfinding improvements:
* Make each path request track whether it needs updating.
* Improve new request handling, reverse order for processing requests.
* Break to handle new requests immediately.
* Make mPathFindThread an integer rather than a bool. Allow two threads.
* For old pathfinding, if the ledger is unspecified, use the PathRequest's RippleLineCache.
* Log new pathfinding request latencies.
* Suspend processing requests if server is backed up.
Pathfinding bugfix. Missing lock.
Concurrent SHAMap code
Use shared lock for SHAMap itself and concurrent map for nodes
Improvements because items in SHAMaps are immutable:

* SHAMapItem::getData is not needed
* SHAMapTreeNode::getItem is not needed
* SHAMapTreeNode::getData is not needed
* No need to copy them when constructing transactions
* No need to copy them when computing map deltas
* No need to copy them in deepCompare
* No need to copy them in SHAMapTreeNode's copy constructor
Reset liquidity before retrying rippleCalc
Add LedgerHolder class, use in LedgerMaster
Handle offers in quality directory but not in ledger