Removing file_io from the package

[dgursoy]

Would it make sense to put all data I/O modules elsewhere such that the package is format independent? This means that we need to provide a common and human readable data structure that is essential for the (analysis and) visualization of data. The data reading and conversion packages can live elsewhere because they are almost always different for each technique/beamline and are very specialized.

We made this choice in the initial development phase of TomoPy by separating the analysis from the data formats. The big plus of this decision is that the main package become lighter and easier to maintain and distribute, because we don't need to support all formats and related software dependencies to read these files.