Fixes test that refered a wrong filename

Also, s/unkow/unknown/g
Adds Palavras part-of-speech tagger to worker POS

Refactors POS worker (now it's a Python module instead of single file)
Returns 'tagset' as a document property (worker POS)
Passes entire document to pos tagger instead of tokens
Fixes broken POS worker tests
Merge branch 'feature/worker-palavras' into develop
Uses absolute path for test data
Fixes all relative filenames in tests
Merge branch 'bugfix/fix-relative-paths-in-tests' into develop
Solve Issue #142, test result depended on version of pdfinfo.

Changes the test to check whether the metadata extracted is a superset of what we expect to have.
Merge remote-tracking branch 'rhcarvalho/bugfix/extract-pdf-test' into develop
Mentions poppler utils as a dependency in the README file

Fixes #141
Documents libmagic as a dependency

Fixes #139
Adds missing comma to README.rst
Stores the mimetype detected during text extraction

Fixes #144
Merge branch 'feature/store-detected-mimetype' into develop