Transactor refactor:
* Allocate transactors on the stack instead of the heap.
* Remove header files and reduce transactor public interface.
Ticket issuing (RIPD-368):
* New CreateTicket transactor to create tickets
* New CancelTicket transactor to cancel tickets
* Ledger entries for tickets & associated functions
* First draft of M-of-N documentation
Ticket integration tests
Cleanups to RPC code
Cleanups and fixes (RIPD-532):
* Properly handle sfWalletLocator field
* Plug a tiny memory leak
* Avoid naked pointers
* Remove unused variables
* Other small cleanups
Create the directory for the debug_logfile (RIPD-551)
Add date to tx command (RIPD-542)
SHAMap performance improvements (RIPD-434):
 * Remove mTNByID
 * Remove mDirtyNodes
 * Much faster traverses
 * Faster snapshots
 * New algorithm for flushing
 * New vistNodes/visitLeaves
 * Avoid I/O if a map is unbacked
The tree cache has to be much larger

This doesn't significantly increase memory consumption because
most entries are pinned anyway.
Make more RocksDB tunables
Add support for universal compaction
Refactor LedgerEntrySet:
* Split adjustOwnerCount to increment and decrement paths.
* Move pathfinding-specific functions out of LedgerEntrySet
* Convert members to free functions
Improve regularity of STObject and STArray (RIPD-448, RIPD-544):
* reduce duplicated code using templates
* replace BOOST_FOREACH with C++11 for loops
* remove most direct calls to new
* limit line length to 80 characters
* clearly identify virtual and overridden methods
* split STObject and STArray into their own files
* name files after the class they contain