add filter method

[benhouse1987]

Hey, it's a good project, will you add json filter functions in the future?

[SriramKeerthi]

I haven't actually considered filter, that's a good suggestion. I need to find out what's a good filter system out there that I can implement here. If you have any suggestions/ideas, please feel free to either reply here or raise a PR if you have code good to go. I'll be happy to work it into this project.