add new app for executing command from BS on mote
add example for rebooting mote remotely
add feature SF_FEATURE_SHELL_OPT in project_conf.h. This allows us to turn on/off shell feature at compiling time
add remote-shell function for handling sending command and command input
modify remote_shell_input() to read packetbuf directly
verify with txpower command. currently able to support command with parameter
enable blink,node_id,txpower,rfchannel
command
add new command: sendcmd. it allows to send command to remote note via serial shell
add msg for incorrect remote shell command. Verified by test
add comments for setting packet cmd attr
Revert 4a08e08..6915fb5

This rolls back to commit 4a08e08e4d6c1e7f4343bc5332324eb1888d2564.
Revert "Merge pull request #24 from s3lsensor/yzliao_v0.2_mac_hdr"

This reverts commit 4a08e08e4d6c1e7f4343bc5332324eb1888d2564, reversing
changes made to 2c849364fe5fb94d167ae6668ce28a955375b7f7.

Conflicts:
	core/net/appconn/app_conn.c
	core/net/appconn/app_conn.h
	hello_world/nullApp.c
	hello_world/project-conf.h
	s3l_rdc/tdmardc.c
Revert 4a08e08..3cb89cc

This rolls back to commit 4a08e08e4d6c1e7f4343bc5332324eb1888d2564.
Revert "Merge pull request #24 from s3lsensor/yzliao_v0.2_mac_hdr"

This reverts commit 4a08e08e4d6c1e7f4343bc5332324eb1888d2564, reversing
changes made to 2c849364fe5fb94d167ae6668ce28a955375b7f7.

Conflicts:
	core/net/appconn/app_conn.c
	core/net/appconn/app_conn.h
	hello_world/nullApp.c
	hello_world/project-conf.h
	s3l_rdc/tdmardc.c
Revert to df3e44ba
resync to dev branch
revise some files to fix incorrect merge
clean code for merge
Merge pull request #25 from s3lsensor/yzliao_v0.2_cmd

Enable command for serial shell and remote shell
fix conflict