add hasVariable function to GenericIO

See merge request !9

remove rebalance_sourceranks function

See merge request hacc/genericio!10

(was added 2 years ago and did not turn out to be useful.
Also causing problems on some compilers, eg on theta)

change default genericio file partitions

See merge request hacc/genericio!8

added initial VELOC support

See merge request hacc/genericio!6

Safe-Guards preventing segfaults for incorrect inputs (python interface)

See merge request hacc/genericio!5

throw an error for missing variables and multiple-defined
 variables if variables are passed to the reader interface

explicitly define the stride for numpy arrays

Updated Docs, New default for python module

See merge request hacc/genericio!4

allow reading single source rank in py module

add more class methods to py interface, whitespace

non-MPI version for (new) Python interface (only affects new_python)

See merge request hacc/genericio!3