Yzliao v0.2 issue 11

This pull request resolves #11 

Details of change:

1. Add new MACRO ```SF_MOTE_TYPE_AP``` and ```SF_MOTE_TYPE_SENSOR``` in ```project-conf.h``` file. See below for how we define the MACROs.

   ```C
  // define sensor type
  #if (SN_ID == 0)
  #define SF_MOTE_TYPE_AP
  #endif /* SN_ID == 0: Access point/Base station*/ 

  #if (SN_ID > 0)
  #define SF_MOTE_TYPE_SENSOR
  #endif /* SN_ID >0: Sensor node*/
   ```

2. Move ```tdmardc.c``` and ```tdmardc.h``` to ```core/net/mac``` and remove/untrack ```s3l_rdc```. This is a historical problem and we are going to update the TDMA files in ```core/net/mac``` directly in the future.

3. Merge hello_world example and reboot example into single folder ```hello_world``` and rename the apps.

4. Update ```build.sh```. Currently, it can be used to compile for different apps. For example, to compile hello_world example,

  ```shell
  ./build.sh make HelloWorld 0
  ```
  Also, TDMA and I2C files copying is removed

5. Untrack some unused files/folders

6. Mirror bug fix and code clean