Ronnie v0.1 testing

copy from @ronniebajwa comment 6e8714b22cabf511c5e2333d0f3deade681a3a45

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This version fixes issues #19,#20. #13 is partially fixed, need to take care of the case when a beacon is missed i.e. continue transmitting on schedule instead of only when a beacon is received.

For #19 , static slot number is defined as a MACRO in tdmardc.h and loaded into a global variable my_slot in tdmardc.c.

For #20 , all timings are now based off the physical (or radio) layer timestamps (see cc2420.c).

The firmware now is capable of supporting from 58 to 1000 sensors, if needed. Default configuration is 1/8s TDMA frame (segment) period, 80 B/s payload, 62 total slots. To try out more slots, decrease FRAMES_PER_SEC to 1.0 and increase TOTAL_TS to 510. More than 500 slots are supported, each slot around 2ms.