This change introduces an autogenerated base58 digit table to remove
the need to find the index of a character in the modified base58
alphabet each time. Additionally, it removes some unnecessary big
integer allocations to cut down on the GC churn.
Before:
BenchmarkBase58Encode 20 64998995 ns/op 0.08 MB/s
BenchmarkBase58Decode 50 35965928 ns/op 0.19 MB/s
Now:
BenchmarkBase58Encode 20 64644351 ns/op 0.08 MB/s
BenchmarkBase58Decode 200 7914748 ns/op 0.86 MB/s
