Add python3 support

This adds python 3 support, but also makes minor changes

- README rewritten using markdown
- Increased default timeout value (was causing timeout often on my device)
- Handle `EVENT_RX_FAIL_GO_TO_SEARCH` event like `EVENT_TRANSFER_TX_FAILED` (raise `TransferFailedException` to support retrying) 
- [PEP8](https://www.python.org/dev/peps/pep-0008/) compliant formatting