v0.2.0 - butterflyknife

• Converted all DB calls to PDO.
• Renamed "permissions" to "groups". Same concept, but using the word "group" suggests that it can be used for more than just access control.
• Implemented "primary group" membership for users. A user can belong to multiple groups, but only one of those will be their primary group.
• Implemented DB-driven home pages for groups. Upon login, a user will be redirected to the home_page for their primary group.
• Implemented templated menus. Every group has a corresponding menu template in models/menu-templates. Upon login, the menu for a user's primary group is automatically loaded and rendered.
• Implemented function-level user authorization. Whenever a function in secure_functions is called, the user_action_permits table is checked to see whether or not that user has access to the function (the action column), conditional on the boolean functions specified in the permits column.
• Organized pages into four categories: account pages, API pages, form pages, and public pages. Public pages reside in the root directory and can be accessed by anyone. Account pages are in the account directory and are only accessible after logging in. API pages are in the api directory, and consist of all the pages that process or fetch data from the DB and interact with the frontend via AJAX/JSON. They are accessible by any logged in user, but will only perform a function if the user is authorized. Form pages are in the forms directory, and consist of pages that generate forms (for creating/updating users, groups, etc.)
• Converted registration page to AJAX.
• Improved installer with site configuration.