15 digit limitation can be wrong

[1simonfish]

I found issue #11, referring to the 15 digit limit.

x = new BigNumber(Number.MAX_SAFE_INTEGER)

should be legal. We're using BigNumber as a replacement for BigInteger, and having to convert legal integers to strings just to convert them to BigNumbers is inefficient. Surely there's a more efficient way to do this?

[MikeMcl]

I've nothing to add to the very long reply I gave in #11. The following will prevent the error.

// There's little reason to have ERRORS true unless debugging
BigNumber.config({ ERRORS: false });

Also, any non-integers or large integers are converted to a string anyway by the BigNumber constructor before the value is parsed, so there is no real inefficiency introduced anyway.

Edit:
From v2.2.0, all integers up to Number.MAX_SAFE_INTEGER are now accepted.