Linter has minimal functionality

Currently, linting only checks for invalid numbers and duplicate keys.

Add support for:

``

The new checks can be added by modifying lintJson.

Also, linting stops early if you `jsonify --lint somejsonfile.json` it should not stop till it gets to the EOF.

We should probably check for overly large numbers, invalid string escapes, or excessively nested structures).

Line and column numbers are hardcoded to -1, indicating no position tracking.

Allow configurable severity levels for issues (e.g., make duplicate keys an error instead of a warning).

Add ANSI/ASCII/UTF-8 colorization for issues.