Wrap RippleCalc into a single function (RIPD-500):

* Change public members of Input and Output to remove trailing _.
* Remove Input constructor and separate flags in RippleCalc to reduce
  duplication and confusion.
* Make calculation result private; add getter.
* Narrow scope of some of the results of calls to rippleCalculate.
Bug fixes and new features for LedgerTool:

* Fix RIPD-509, RIPD-514, RIPD-519, RIPD-525, RIPD-527, RIPD-529,
  RIPD-530 and RIPD-531.
* Protect people from ledger-spew and remove cruft.
* Better error messages and handling.
* Cache command lists or clears ledger cache.
* Better ledger summaries.
* Offline mode.
HTTP message and parser improvements:
* streambuf wrapper supports rvalue move
* message class holds a complete HTTP message
* body class holds the HTTP content body
* headers class holds RFC-compliant HTTP headers
* basic_parser provides class interface to joyent's http-parser
* parser class parses into a message object
* Remove unused http get client free function
* unit test for parsing malformed messages
HTTP(S)-RPC server improvements (RIPD-489, RIPD-533):
* Correct handling of Keep-Alive in socket handlers
* Report session history in print command