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* **Breaking change** Labels associated with features data must be sorted in increasing order. This is
convenient to use with timestamps and improve reading huge datasets with long labels.
* **Breaking change** Appending new data to an exisiting item is no more allowed. Suppose a h5f file with 3 items ['a', 'b', 'c'], in 1.1 it was possible to append 3 items ['c', 'd', 'e'], giving a file with the 5 items ['a', 'b', 'c', 'd', 'e'], where the item 'c' being the concatenation of original and appended data. That facility was messy and is removed in 1.2.
* Bugfix when writing unidimensional features
* Bugfix when reading from time/to time in Reader
* Safely overwrite existing groups in h5features files with mode=’w’
* Now more than 100 test cases