Added dest_dir key under mozilla-addon-sdk overview in README.md
fix dest_dir default value in README.md
change dest_dir custom value example to 'build_tools/' in REAMDE.md
bump version to 0.4.0-dev
download latest stable Addon SDK released by default (and removed targz dependency)
Merge branch 'feature/default-download-latest-stable'
FEATURE: added strip_sdk option to mozilla-cfx-xpi tasks (true by default)
FIX: 'strip_sdk == false' should bundle and force use of the bundle sdk modules
fix gruntfile and tests