[#14] Log events locally and submit later with cron

Log events to a local file and provide method for sending them to KISSmetrics on a schedule.

Usage example:

````php
$log_dir = '/path/to/directory';

// Register an event, and log it.
$km = new KISSmetrics\Client($api_key, KISSmetrics\Transport\Delayed::initDefault($log_dir));
$km->identify($id);
// Set properties etc. then submit.
$km->submit();

// Ship logs ...
$km_transport = KISSmetrics\Transport\Delayed::initDefault($log_dir);
$km_transport->sendLoggedData();
````

Resolves #14