§3 Dieudonné algebras

More homological algebra and our main examples.
Define Dieudonné algebras (Definition 3.1.2). Discuss Examples 3.1.8,
3.2, and that of the completed de Rham complex as a Dieudonné algebra
(Variant 3.3.1, Corollary 3.3.8). Discuss Propositions 3.4.2 and 3.4.3.
Prove Propositions 3.5.5 and 3.5.8, and Corollaries 3.5.9 and 3.5.10.