Add position sensor block

[araobp]

Use hall sensors to detect movement of a thing with a small magnet.

• Out => In: 1
• In => Out: 0

If the number of hall sensors is 6:

%21:UINT8_T:0,0,1,0,0,0,0,0
%21:UINT8_T:0,0,0,1,0,0,0,0
%21:UINT8_T:0,0,0,0,1,0,0,0

This block does not generate time-series data. See also #5.

[araobp]

This commit 7ec68ee for PIC16F1825.

[araobp]

The implementation for PIC16F1829 requires a bug fix:

   for(i=0; i<AINS; i++) {
        if ((value & mask) == 0) {  <== this is the bug.
            analog_in[i] = 0;
            position[i] = 0;
        } else {
            analog_in[i] = ANALOG_IN[i];
        }
        mask = mask << 1;
    }