Add support for CSV arrays in RPN calculator.

This feature may be useful in combination with the merge operation
that appends keys together with a "," separator.
Replace if-chain with switch on String object.

Java 7 supports switch statements on Strings.
Addition of "vector" calculator operation.

The "vector" operation modifies the behavior of the next
operator to pop all elements on the stack and push a
single element onto the stack. "vector" is currently implemented
for addition, multiplication, min, and max operations. This
alleviates the need for N forms of vector operations.
Merge pull request #78 from addthis/calc-aggregates

Add support for CSV arrays in RPN calculator.