Prepare/Escape SQL queries

[TomboFry]

Currently, I am doing no preparation of the queries sent to the SQLite database. At least the following should happen:

• [x] Escape all quotes, or encode them into HTML entities
• [x] Post slug should accept alphanumeric, hyphen, and underscore characters ONLY
• [x] Post tags should accept alphanumeric, space, hyphen, and underscore characters ONLY
• [x] Post type should accept alphabetic characters ONLY