Merge pull request #9 from f4nt/tablib

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I thought I was going to wait til later to do this, but once I got started I couldnt stop myself I guess. I believe this fixes the row limit issues that I mentioned earlier by adding XLSX support. Ive tested it up to 75k rows. Believe the tests and setup.py should be squared away properly as well. Im a bit concerned about the pane freezing stuff, as thats completely undocumented in openpyxl. Truth be told, I barely even know what that functionality does. I hate spreadsheets :)

Anyways, let me know if you want any changes or anything made. Dont have to worry about hurting my feelings or anything!

Conflicts:
	tablib/core25.py
	test_tablib.py

test_tablib.py

@@ -222,6 +222,7 @@ class TablibTestCase(unittest.TestCase):
         data.csv
         data.tsv
         data.xls
+        data.xlsx
         data.html
 
 
@@ -234,6 +235,7 @@ class TablibTestCase(unittest.TestCase):
         book.json
         book.yaml
         book.xls
+        book.xlsx
 
 
     def test_json_import_set(self):