Disable module inspection by default

[wata727]

Fixes #198, #248

Disable module inspection by default, as described in #248.

The change allows you to perform an inspection without required additional steps. As before, if you want to do module inspection, perform with the --module option:

$ tflint --module

You can also enable/disable the option from a configuration file as follows:

config {
  module = true
}