WHO and exon resolutions

[mmaiers-nmdp]

This adds "W" and "exon" as redux levels
"W" is an expanding type (like MAC and XX) in that finds all WHO alleles consistent with the input.
"exon" is a reducing type, it expects input that is already exon (3field) resolution or higher (4 field) and reduces it to 3 field.

To covert 2-field/MAC/XX to exon/3-field resolution it requires calling redux_gl twice: once at W level to expand and then at exon level to reduce the output to exon/3-field

[mmaiers-nmdp]

Before merging there are some issues with PR #103

1. it doesn't work the first time the sqllite3 database is created but it does the 2nd time when it is read
2. v2 support was removed because it led to infinite recursion and I didn't see a good general solution
3. test cases are needed for "exon" and "W" resolution

[pbashyal-nmdp]

Following changes to the PR merged:
- Fix issue with returning who_group
- gc only for Python >= 3.9
- lru_cache size can be parameterized with max_cache_size
- Add tests for W and exon redux_types

[pbashyal-nmdp]

Closing with commit 3809696