sw-precache and implicit index.html rewrites

[jeffposnick]

Many servers are configured to handle a request for a bare directory URL as being equivalent to the request for index.html within that directory.

It's possible, but not intuitive, to handle this using the dynamicUrlToDependencies parameter. This approach also forces you to list entries for every directory that has an implicit index.html rewrite.

At the very least, the docs should clarify this behavior. Better, sw-precache should add a new option to configure what bare directories get rewritten to (e.g. index.html,index.php,index) and should automatically handle serving the appropriate file without the need for [dynamicUrlToDependencies`] mappings.