customMatcher support

[fmal]

Describe the bug
I can't get the plugin to work when i specify customMatcher such as:

{
  "name": "typescript-plugin-css-modules",
  "customMatcher": "\\.css$"
}

When i leave it off then everything works fine.

To Reproduce
Add "customMatcher": "\\.css$" and use a filename without the .module part (justAFile.css)

Additional context
I quickly browsed the source and noticed that isRelativeCSS helper actually uses the default isCSS predicate: https://github.com/mrmckeb/typescript-plugin-css-modules/blob/develop/src/helpers/cssExtensions.ts#L6. I guess passing overwritten isCSS to isRelativeCSS would solve this issue.

Will look into that later in the evening and submit PR if that is the case 😃

BTW. nice plugin!

[mrmckeb]

Thanks again @fmal. This is now released.

On your other issue, I think we can discuss here: #10.