Add support for glob syntax in {css,js}_files lists

[sisp]

I'd like to be able to list files to minify using glob syntax, which doesn't seem to be supported yet. For instance:

plugins:
  - minify:
      css_files:
        - assets/css/**/*.css

I have several CSS files, many contain page-specific styles, so the list grows with more pages. Instead of maintaining a hardcoded list of files, I'd prefer using glob syntax.

The same applies to JS files, of course.

WDYT?

[AdrianDsg]

This should be possible by iterating through file_paths in line 84 in

mkdocs-minify-plugin/mkdocs_minify_plugin/plugin.py

Lines 83 to 85 in e6fe363

	file_paths = [file_paths]
	for file_path in file_paths:

looking for * and resolving the globs by using pathlib.Path.glob() and extending file_paths with the results.

[AdrianDsg]

I just revisited this topic again and came up with a working proposal in #37. As mentioned in the PR the code might be not as efficient and clean as possible so please feel free to share your feedback to improve the code quality.