v0.4.8 Better support for nested fields and more supported predicates

Previously predicates on nested (and deeply nested) fields were not properly supported. This release adds support for filtering on struct sub-fields or deeply nested structs.

We also add support for more filter predicates and fixed a regression in NULL handling for string columns.

What's Changed

• Fix nested schema merge by @changhiskhan in #836
• Fix nested field filtering by @changhiskhan in #837
• Fix Projection for struct fields by @changhiskhan in #844
• [Bug] Calculating the nulls from position slices in chunks. by @eddyxu in #846
• Add tests for is_NULL, is_not_null, and invert in filter by @eddyxu in #847

Full Changelog: v0.4.7...v0.4.8