Huge memory consumption with large JSON files

[eMPee584]

I just tried to diff two firefox memory reports (73MiB each) and jdiff exploded, had to shoot it down at about 5GiB of RAM usage.. You may try yourself, the reports can be generated on the internal about:memory page.

[corytodd]

Related to #49

The algorithm does not scale very well and appears to run in O(n^2) time. I don't have any immediate suggestions other than perhaps preprocessing the output into smaller sections and diffing those. If you have ideas on alternative approaches we'd love to hear them!