Generate sourcemap if '--map' option is specified

Currently we cannot generate sourcemap even if we specified
`-m` or `--map` option to `coffee-args-compile`, because sourcemap
option cannot be used with `--print`(`-p`) option together.
We use `--print` option for compiled JS  without writing JS file.

So coffee-mode generates sourcemap at another phase if user specifies
`--map` option.