doc: fix nightly generation (#71)

* fix: add a temporary exception for a new lint

ref: rust-lang/rust#82450

there will probably be a cleaner fix at some point (or even a change in
how the nightly cfg is implemented)

* fix: update a broken link in doc

Author: imrn99

honeycomb-core/src/cmap2/structure.rs

@@ -5,6 +5,9 @@
 
 // ------ IMPORTS
 
+#[cfg(doc)]
+use crate::NULL_DART_ID;
+
 use super::CMAP2_BETA;
 use crate::{AttrSparseVec, CoordsFloat, DartIdentifier, Vertex2};
 use std::collections::BTreeSet;

honeycomb-core/src/lib.rs

@@ -18,6 +18,7 @@
 // ------ CUSTOM LINTS
 
 // --- enable doc_auto_cfg feature if compiling in nightly
+#![allow(unexpected_cfgs)]
 #![cfg_attr(nightly, feature(doc_auto_cfg))]
 // --- some though love for the code
 #![warn(missing_docs)]