[Tests] Added tests for ints with values over 53bits

[ericpassmore]

By default JS number handle values up to 53bits. Added two serialization and deserialization tests showing eosio-core supports UInt64 and Int64.

Resolved #48

[jnordberg]

Thanks! Although integers are already tested extensively in ./test/integer.ts, perhaps you missed that? These tests does not change test coverage over the integer types.

I'm not opposed to adding these tests anyways if you feel they add value. The reliance on BigInt has to go though as well as the direct import of '../src' in the test files since both those things will break the browser tests

[ericpassmore]

LOL, its a pull request with little value. I'll go ahead an close it.

I did the test for my own learning, and double-check. I didn't find any serialization/deserialization tests for Int64, and I decided to create the PR. Thanks for taking a look.