* Apply bytesize and number of param limits in QueryParser

The param limit is 4096, chosen because it matches the existing
multipart limit.  The bytesize limit is 4MB.  These limits should
substantially exceed what almost all applications need, though
there will likely be applications that require higher limits.
Allow overriding the limits on a per-QueryParser basis via the
constructors, and allow overriding the default limits with
environment variables RACK_QUERY_PARSER_BYTESIZE_LIMIT and
RACK_QUERY_PARSER_PARAMS_LIMIT.

Add new Rack::QueryParser::QueryLimitError to raise in case one
of the limits are exceeded, and make ParamsTooDeepError an
alias to, since that is also a case where a limit is exceeded.
This allows code that already rescues ParamsTooDeepError to
automatically handle these other limits as well.

* Update CHANGELOG.

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Co-authored-by: Samuel Williams <samuel.williams@oriontransfer.co.nz>