Ensure marmottawrapper has minimal external dependencies

* Use `#{app_root}/marmotta` as the data directory...for real
* `marmottawrapper` now no longer depends on `curl` and `unzip`
    * `rake marmotta:fetch` uses `open-uri` and grabs a tarball
    * `rake marmotta:install` uses `Archive::Tar::Minitar` and `GZip`
* Update README to describe Marmotta configuration conventions
Merge pull request #12 from dpla/simplify-external-dependencies

Ensure marmottawrapper has minimal external dependencies
Add rake tasks to non-Rails projects

Marmottawrapper tasks were previously only added to rails projects,
this adds them to enviornments where Rake exists, but Rails does not.
Merge pull request #13 from dpla/feature/non-rails

Add rake tasks to non-Rails projects
Bump version to 0.0.6