Implement a check for dependencies in mat2

Example use:

```
$ mat2 -c
Dependencies required for MAT2 0.1.3:
- Cairo: yes
- Exiftool: yes
- GdkPixbuf from PyGobject: yes
- Mutagen: yes
- Poppler from PyGobject: yes
- PyGobject: yes
```

This should close #35

1 files changed, 8 insertions, 0 deletions

diff --git a/tests/test_libmat2.py b/tests/test_libmat2.py
index cb37985..fa7e281 100644
--- a/tests/test_libmat2.py
+++ b/tests/test_libmat2.py
@@ -7,6 +7,14 @@ import zipfile
 import tempfile
 
 from libmat2 import pdf, images, audio, office, parser_factory, torrent, harmless
+from libmat2 import check_dependencies
+
+
+class TestCheckDependencies(unittest.TestCase):
+    def test_deps(self):
+        ret = check_dependencies()
+        for key, value in ret.items():
+            self.assertTrue(value)
 
 
 class TestParserFactory(unittest.TestCase):