curve: fully migrate to 2018 module conventions (#844)

Enforced via the newly added `clippy::mod_module_files` lint.

Previously a mixture of 2015 (`mod.rs`) module files along with
the 2018 `foo.rs` and `foo/` approach.

All of the toplevel modules (`edwards`, `field`, `montgomery`, and
`scalar`) were using the 2018 convention, except for `backend`,
`ristretto`, and the recently added `lizard` were using the 2015
convention.

This renames the files so everything follows the 2018 convention, and
applies the afforementioned clippy lint which will error if anyone tries
to add new files using the 2015 convention.

curve25519-dalek/src/backend/serial/fiat_u32.rs

@@ -17,10 +17,10 @@
 //! This uses the formally-verified field arithmetic generated by the
 //! [fiat-crypto project](https://github.com/mit-plv/fiat-crypto)
 
-#[path = "../u32/scalar.rs"]
+#[path = "./u32/scalar.rs"]
 pub mod scalar;
 
 pub mod field;
 
-#[path = "../u32/constants.rs"]
+#[path = "./u32/constants.rs"]
 pub mod constants;

curve25519-dalek/src/backend/serial/fiat_u64.rs

@@ -19,10 +19,10 @@
 //! (allowing the CPU to compute two carry chains in parallel).  These
 //! will be used if available.
 
-#[path = "../u64/scalar.rs"]
+#[path = "./u64/scalar.rs"]
 pub mod scalar;
 
 pub mod field;
 
-#[path = "../u64/constants.rs"]
+#[path = "./u64/constants.rs"]
 pub mod constants;

curve25519-dalek/src/backend/vector.rs

@@ -9,7 +9,7 @@
 // - isis agora lovecruft <isis@patternsinthevoid.net>
 // - Henry de Valence <hdevalence@hdevalence.ca>
 
-#![doc = include_str!("../../../docs/parallel-formulas.md")]
+#![doc = include_str!("../../docs/parallel-formulas.md")]
 
 #[allow(missing_docs)]
 pub mod packed_simd;

curve25519-dalek/src/backend/vector/avx2.rs

@@ -9,7 +9,7 @@
 // - isis agora lovecruft <isis@patternsinthevoid.net>
 // - Henry de Valence <hdevalence@hdevalence.ca>
 
-#![doc = include_str!("../../../../docs/avx2-notes.md")]
+#![doc = include_str!("../../../docs/avx2-notes.md")]
 
 pub(crate) mod field;
 

curve25519-dalek/src/backend/vector/ifma.rs

@@ -7,7 +7,7 @@
 // Authors:
 // - Henry de Valence <hdevalence@hdevalence.ca>
 
-#![doc = include_str!("../../../../docs/ifma-notes.md")]
+#![doc = include_str!("../../../docs/ifma-notes.md")]
 
 #[allow(missing_docs)]
 pub mod field;

curve25519-dalek/src/lib.rs

@@ -24,6 +24,7 @@
 //------------------------------------------------------------------------
 #![cfg_attr(allow_unused_unsafe, allow(unused_unsafe))]
 #![warn(
+    clippy::mod_module_files,
     clippy::unwrap_used,
     missing_docs,
     rust_2018_idioms,