Metacrawler

Added
- limiting;

Added
- cap `value` attribute for `Field` class;

Added
- `Field` type validation;

Updated
- collapsing list `Field` to single field if using pagination;
- default `Crawler.paginate` pagination if using pagination;

Added
- optional collapsing single field in `Crawler` class;

Fixed
- using pagination;

Added
- default output;

Updated
- project management (template, copy method);

Removed
- `Item` class;
- Python < 3.4 support;