Avalon2: add polling delay option, long coinbase support, LED status on API, change overheat from 88 to 98
Avalon2: add more comments on Avalon2 options
Merge pull request #637 from Canaan-Creative/rebase

Avalon2: add polling delay option, long coinbase support, LED status on ...
Add iic interface
Use xfer to exchange iic data
Add Avalon3.5 MM version pattern
Make api-example can parse long API message. Thanks to Mikeqin