remove is_file check for .h5 file in CoRe_h5 constructor
Otherwise one can't instantiate a CoRe_h5
object with the defaults.
This makes the following lines from the watpy_wave.ipynb
tutorial run
ch5 = CoRe_h5(bamsim['pre-release-folder']) # write .h5 to mysim['pre-release-folder'] ...
ch5.create(path=bamsim['pre-release-folder']) # ... all the CoRe .txt files in mysim['pre-release-folder']
Not 100% sure if that is the right fix.