[v1.10] support arbitrarily big numbers (fix issue #4)

new user preferences:
 * "Use non-native JSON parser to support numbers that are too large to represent using primitive JavaScript data types"
 * "Display JSON syntax error when encountered by the JSON parser"

the available (optional) non-native JSON parser is:
  https://github.com/sidorares/json-bigint
which uses:
  https://github.com/MikeMcl/bignumber.js