[NFR] FirePHP Log Adapter and Formatter

The idea was taken from the [https://github.com/phalcon/incubator/tree/master/Library/Phalcon/Logger](incubator).

The adapter is meant to send messages to FireBug with FirePHP extension enabled.

This implementation differs from the incubator's:
  * `_initialized` and `_index` properties are static — if by accident the user instantiates two loggers, FirePHP will be very confused;
  * very long messages are split into 5KB chunks so that Firefox be able to read the headers properly.

Bonuses:
  * much shorter version of `Phalcon\Logger\Formatter::getTypeString()`
  * results returned by json_encode() are always NUL-terminated (otherwise Zend Engine complains loudly if PHP is built with debugging support)