Arinfopy

- Added `getSlice(variable, slice, deadline)` to select a specific deadline and slice (for 3D variables) of the requested variable. This method should also improve the efficiency of 3D data recovery.

- Stripping whitespaces from variables names.

- The deadline argument of `getRecord7` is 1-based. If `deadline=0` is passed to the function a `ValueError` is raised.

- Many bugfixes and code cleanup.

- Converted to python3 (still compatible with python2).

- All summary informations are read.

- Added `minmax` option.

- It can be called by other modules.

- Added method to get the list of deadlines.

- First basic working version.