introduction of pathlib.Path

use pathlib.Path class to specify relative paths. also added as an accepted input for the dataset classes' filepath specifier.

tests/test_dataset.py

@@ -6,7 +6,8 @@ import numpy as np
 import icartt
 
 # working directory, example files
-wd, fns = pathlib.Path('.'), pathlib.Path('./examples').glob('*.ict')
+wd = pathlib.Path(__file__).parent
+fns = (wd/'examples').glob('*.ict')
 
 def compareFiles(fn, strIn, strOut, skiplines=0, nlines=-1): # pragma: no cover
     strOut.seek(0)