Revert "Merge pull request #200 from sigp/new-structure"

This reverts commit d7a3545be1, reversing
changes made to 1da06c156c.

eth2/state_processing/src/lib.rs

@@ -0,0 +1,10 @@
+mod block_processable;
+mod epoch_processable;
+mod slot_processable;
+
+pub use block_processable::{
+    validate_attestation, validate_attestation_without_signature, BlockProcessable,
+    Error as BlockProcessingError,
+};
+pub use epoch_processable::{EpochProcessable, Error as EpochProcessingError};
+pub use slot_processable::{Error as SlotProcessingError, SlotProcessable};