Merge pull request #2 from kobuki/master

implemented LOOP parameter (number of packets)
Added preliminary DS3231 RTC support.
Super ugly, but DS3231 alarm interrupts now hooked up.
Fix wind calculation.
Fixed ISSRx for Rob G. Simplified wind calc. Thx Kobuki!
Convert packetStats array to a struct.
Start of conversion of loop packet to a struct.
Convert loopData array to a struct.
Add SETPER command and basic EEPROM stuff in prep for archiving to flash.
Reduce number of bogus compiler warnings.
- added TX mode flag setting (can be used by standalone sensor transmitters)
- added user callback hook for additional processing of received packet data (used by multiple receivers code, in progress)