The RippleCalc saga continues.

* Comments from RippleCalc learning session 2014/06/11.
* Better types Currency and Account using tagged uint160s.
* Helper functions isXRP, toString and operator<<.
* Move "zeroed" function onto STAmount.
* Rename some members of path::Node for clarity and to show they are members.
* Rename some colliding local variables to show they are not members.
* Inline many aliases to object variables to reduce programmer memory load.
* More usage of Currency, Account, isXRP, and comparisons with zero.
* Rename some functions and source files in RippleCalc to better reflect actual meaning.
* Much 80 column reworking.
* Usage of new default operator<< for debugging statements.