feat(crypto): expose api modules

Currently the API modules are hidden to the crate scope.

In order to avoid global permissive allows, they can initially be
exported, and tweaked to local scopes as they get implemented, finalized
and tested.

Related to #3

crypto/src/hash/mod.rs

@@ -11,7 +11,7 @@ pub type Digest = ::Digest;
 // ================================================================================================
 
 #[inline(always)]
-fn exp_acc<B: StarkField, const N: usize, const M: usize>(base: [B; N], tail: [B; N]) -> [B; N] {
+fn _exp_acc<B: StarkField, const N: usize, const M: usize>(base: [B; N], tail: [B; N]) -> [B; N] {
     let mut result = base;
     for _ in 0..M {
         result.iter_mut().for_each(|r| *r = r.square());

crypto/src/lib.rs

@@ -3,8 +3,8 @@ pub use winterfell::math::{
     ExtensionOf, FieldElement, StarkField,
 };
 
-pub(crate) mod hash;
-pub(crate) mod merkle;
+pub mod hash;
+pub mod merkle;
 
 // TYPE ALIASES
 // ================================================================================================