Improve the description for several filesystem matchers.#228

Draft

thomir wants to merge 2 commits intotesting-cabal:masterfrom

thomir:improve-matcher-descriptions

Commits on Apr 15, 2016

Initial proof-of-concept to improve the output of filing matchers.
thomir
committed

Commits on May 1, 2016

Fix PathExists, DirExists & FileExists matchers to have a more helpful __str__.
thomir
committed