Prevent -f from dumping the whole file before following

- Thanks to Avianna for the bug report
Stop --count from prepending a bunch of junk to the output JSON

- Makes consuming it from another script easier

- Thanks to Avianna for the suggestion
Allow --count to accept expressions, just like --grep and --map

- One of the reasons this is useful is you can fetch arbitratily nested items from the data section

- Thanks to Avianna for the suggestion
In the event of a --map or --grep expression failing to compile, include the faulty expression in the error message