Create benchmarks

[hasufell]

We need to observe memory behavior between abstract-filepath and current libraries, e.g. when listing a few million files in some directories.

Also need to observe behavior wrt ShortByteString splitting etc, which are copy operations.

[mgajda]

Testing these use cases may cover a lot of potential trouble spots:

1. Making generator for all valid file paths on each platform starting from temporary directory.
   Creating a directory tree for the path, and and removing it.
   May be checked with both relative and absolute paths to compare.
2. Listing a directory with millions of files.
3. Searching through a large directory tree (like that of GHC or Linux.)
4. Counting files that match a glob pattern within a large directory, or a directory tree.