0.5.5 (19.10.2016)
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* numerous bugfixes
* change behavior of `if_val()` - now it dowsn't copies old values by default. There are 'other' and 'copy' instead of dots.
* add `%n_i%`, `%n_d%` - names intersection and diffs
* add `add_rows` function
* add `keep` and `except` functions for selecting/dropping columns in data.frames
* add 'where' for filtering dataset
* add `sort_asc` and `sort_desc` functions for sorting data.frames

0.5.1 (07.07.2016)
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* initial release 

