#106 improvements of pitch command

[Shikano Motoki]

The pitch command has room to improve.

1) Outputting the variables used to the pitch extraction algorithms:
The pitch command includes the three pitch extraction algorithms, e.g., RAPT, SWIPE, and REAPER. These algorithms have their own variables used to compute F0 values. Although sometimes the variables are useful for signal processing, it is unreasonable to handle all of them in the pitch command. Supporting only a few important variables in Level-2 options is a simple
solution.

2) Flexible tuning:
In the pitch command, the search range of F0 values and the voiced/unvoiced threshold can be changed to obtain an accurate F0 counter. Each of the pitch extraction algorithms have the other their own tuning parameters, but they cannot be available in the command in order to supply the consistent command-line options. This prevents to exploit the algorithms. It may be better to wrap the algorithms separately.