This reverts commit 49d91d08.

This reverts commit fe87cd24.

This reverts commit 34f47e34.

This reverts commit 5fb6d7c9.

This reverts commit dc7d76ae.

This reverts commit a45125f0, reversing
changes made to bd4d8c3b.

This reverts commit c67762a7, reversing
changes made to b12a0eb3.

Eventually the goal is to rewrite and replace all uses of VectorView
with some form of seq_view.

Due to the identity: gamma_p(a,z) + gamma_q(a,z) = 1
anywhere that computes 1-gamma_p(a,z) can be rewritten as gamma_q(a,z).
This should reduce roundoff when the return value is near zero.

For example, this should improve the accuracy of gamma_ccdf_log(16, 3, 3).