Add automatic range-checking and type-casting for readJson

This change allows numerical types to be passed to readJson
with the desired type.  They will then be automatically
range-checked and cast to that type.

Tested: Requested variables of type uint64_t, uint8_t, int,
int16_t, and int8_t and confirmed that the range was correctly
checked for each.

Change-Id: Ia55cb03ba2c4321a7de35a7c7b566980a72c5449
Signed-off-by: Jason M. Bills <jason.m.bills@linux.intel.com>