Nextnanopy

Assistant is updated, bugs fixes and updated functionality of sweep.

* input files now can be execute in parallel throug nextnanopy.inputs.ExecutionQueue class
* Sweep uses ExecutionQueue and executes several simulations in parallel if parallel_limit>1 in Sweep.execute_sweep(parallel_limit = n)

Details of parallel execution in nextnanopy here: https://github.com/nextnanopy/nextnanopy/blob/master/docs/examples/Example4_Sweep_to_automate_the_execution.ipynb
https://github.com/nextnanopy/nextnanopy/blob/master/docs/examples/Example_advanced1_ExecutionQueue_for_parallel_execution.ipynb

nextnanopy.Sweep.save_sweep has parameter round_decimal to limit round of digits in the folder names. Deafault round_decimal = 8

* Default .dat loader of nextnanopy.DataFile was changed. Before x,y,z and position were coordinates, anything else recognized as variables. Now first column of the '.dat' file is recognized as coordinate, all other columns are variables.
* Demo: parser of the whole input file for nextnano++. Raise error if file contains incorrect number and order of parentheses '{}'