Fix subscribing to "real time" transactions.
Fix a pathfinding bug
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
PathRequests object to own all path requests.
Add directory and order book iterators
This should fix the crossed order book bug.
* Change OfferCreate::takeOffers to use new iterators
* Change NetworkOps::getBookPage to use new iterators
[FOLD] Make offerDelete more robust.
[FOLD] Make fillItems more robust
Handle offers in order books but not in the ledger proper
[FOLD] Functions to get the index of the current directory itself
[FOLD] If we find an offer in the book but not the ledger, deindex it
[FOLD] cleanup offerDelete
[FOLD] cleanup
[FOLD] dirDelete cleanup
[FOLD] remove LES::intersect