simplify sending requests, small improvements, documentation updates

- simplified access to logs and reports endpoint (fix #6);
- changed send() inteface, added sendLogs() and sendReports() wrappers
(fix #6);
- clear data after sending them to endpoint fixes issue of sending the
same data twice;
- removed remaining references to publicApiKey;
- updated Yii extension to use new sending approach;
- updated documentation;