Bug fixes

• Fixes some issues with defining the filenames of external links. Now, a new keyword, abspath, has to be set to True when initializing a link if the absolute file path is to be used. Otherwise, the relative file path with respect to the file containing the link is stored, whether the input file path is absolute or not. The default value is abspath=False.
• Fixes some issues related to defining floating point slices when the axes are stored as bin boundaries rather than bin centers.