The regular expression is copy & pasted form the one in the spec.
The change suggested in #171 and integrated was improper.

Closes #290

Backport of caeefd8.

This addresses the following items:

==== Parse time of excessively deep nested or indented documents

Parsing these documents is non-linear; limiting stack depth to 10,000 keeps parse times of pathological documents sub-second (~.25 seconds in benchmarks)

==== Alias node expansion limits

The current limit allows 10,000% expansion, which is too permissive for large documents.

Limiting to 10% expansion for larger documents allows callers to use input size as an effective way to limit resource usage. Continuing to allow larger expansion rates (up to the current 10,000% limit) for smaller documents does not unduly affect memory use.

This change bounds decode operations from alias expansion to ~400,000 operations for small documents (worst-case ~100-150MB) or 10% of the input document for large documents, whichever is greater.

The problem does not affect v3.

This should simplify the logic and significantly improve
performance in edge cases as found and reported on #537
by CJ Cullen.