Improve logging of transformed names

[sholladay]

Since I upgraded this plugin to 1.x, building my app now logs hundreds of lines like these:

Exported "nav-left" as "navLeft" in lib/css/nav-bar.css
Exported "nav-search-wrapper" as "navSearchWrapper" in lib/css/nav-bar.css
Exported "nav-user" as "navUser" in lib/css/nav-bar.css
Exported "spinner-container" as "spinnerContainer" in lib/css/common.css
Exported "error-container" as "errorContainer" in lib/css/common.css
Exported "header-upload-container" as "headerUploadContainer" in lib/css/header.css
Exported "background-image" as "backgroundImage" in lib/css/header.css

... which is super useless.

The reason this happens is because I camelcase the exports using the namedExports option, to avoid the weird $__$ stuff that this plugin does by default. Here is my config:

postcss({
    modules : true,
    namedExports(name) {
        return camelcase(name);
    }
})

As discussed in #64 (comment), camelcasing should probably just be the default behavior. Presumably, at that point we would expect the plugin to only log if it encountered an export that would be a reserved word in JS.

In the meantime, while I'm waiting for a 2.x version to be released, I was thinking this plugin should skip these logs when namedExports is a function, as the user is fully controlling the name transformation, so shouldn't need to be told about it. I think it's okay to keep logging when it's true, as the default algorithm is unintuitive for now.

Alternatively, there could be an option to disable these logs, but that just increases the API surface unnecessarily IMO. And when 2.x comes, it would be even less necessary.