Added sleep support for MCP2515 + MCP2551. This way, you can reduce the power consumption of a complete node down to around 240uA!
Changes:
- Reintroduced gpio support from commits 43521de/bac66d1 (adlerweb, 15/01/2018) and corrected the errors
- Introduced advanced sleep support based on https://github.com/coryjfowler/MCP_CAN_lib/pull/10/files
- added example code (receive_sleep and send_sleep)
- tested everything