change channel update for gecko 32 ( 2.0 )

Adding example for console

Added check return code for shallow_flash.sh
fix #215
Support auto flashing v2.0.0 from pvtbuilds.
Merge pull request #218 from davehunt/auto-flash-2.0

Support auto flashing v2.0.0 from pvtbuilds.
Merge pull request #217 from nhirata/Gecko32Update

Gecko32 update for change channel script.
Update the usage of shallow_flash.sh for MAC user.

Fix #213
Merge pull request #219 from askeing/add_mac_usage_for_shallow_flash

Update the usage of shallow_flash.sh for MAC user.
update the desktop b2g download link
Merge pull request #220 from askeing/master

update the desktop b2g download link