Add idxfileparser.py
Add unit tests for idx.py
Implement idx._find_dimensions, add docstrings
Update for python 3 and new idx design

idx no longer writes to files, it only processes bytes
Fix issue where idx test uses wrong bytes object

Forgot to include the sizes of each dimension
Change count_dimensions to find_dimensions

Return a list of dimension sizes, rather than the number of dimensions.
Implement find_dimensions
Complete list_to_idx