Add more filtering parameter options

[pushshift]

Create filter options to grep comment bodies and submission titles/selftexts. Also filters for fields such as over_18 (nsfw), self posts, etc. Also filters for comments containing links, or comments that are replies only or top level comments only.

Possible filters include:

Boolean: over_18, self_post, top_level_comment, etc.

String: body_contains, title_contains, selftext_contains