Use search pattern and options for EnumerateFiles

```EnumerateFiles``` has an overload which allows a search pattern and search options. Swapped it to use this with the default search pattern of '*' and the ```SearchOption.AllDirectories```, which searches the current directory and it's subdirectories.
Merge pull request #120 from sgrassie/search-all-directories-for-posts

Allow posts to be stored in subdirectories