Avoid unnecessary BOM checks
Avoid unnecessary BOM checks

Overhead of method calls can be significant when parsing very large
JSON files. Only checking for the BOM at the first four characters of
a file makes for an easy performance improvement.

The difference in parsing speed is negligible for files like
'tests/ratherBig.json'. When parsing a 50+ megabyte single line of
JSON with lots of string data and using a light-weight listener, this
improvement can cut the parsing time in half.

salsify/jsonstreamingparser