Added --sourcemap flag

--sourcemap flag is enabled as of compass.alpha.17

https://github.com/chriseppstein/compass/commit/7cd79d53d61ff02a04dd19d5fd1bd3ac6f542416
add sourcemap option

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>
Merge branch '33'
add sourcemap default value

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>
Add support sourcemap readme.

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>