Add option for collecting all keywords in the summary to the documentation
Initial test of adding all keywords in the header.
Implement collecting all leader keywords in table

Closes #125, but there are a couple unresolved issues still. See #148, #149
Change case of all summary table columns to lower

This matches the behavior currently enforced by ImageFileCollection.
Refactor tests to minimize the number of simbad lookups needed
Check that ImageFileCollection summary is always a masked table

Closes #148
Make test for accumulating all keywords more extensive
Use user-provided case for clump names in ImageFileCollection summary

Closes #149
Merge pull request #150 from mwcraig/grab-all-keys

Grab all keys