Collect pandas (and other) weird memory usage cases

[ianozsvald]

• Memory usage increasing with df.dropna(inplace=True) and df.head() pandas-dev/pandas#11050
• Variable deletion consumes a lot of memory pandas-dev/pandas#17092
• High memory peak when MaskedArray creates a mask numpy/numpy#6732
• https://github.com/liushuchun/pynote/tree/master/slots_magic (use case)
• https://github.com/jni/streaming-talk (use case)
• https://github.com/ianozsvald/ipython_memory_usage/blob/master/src/ipython_memory_usage/examples/example_usage_np_pd.ipynb (my example for pandas del vs drop via Jamie Brunning)