feat: check URL fragments

This implements URL fragment checking. Parsing is expanded to also
collect values of all `id` attributes.

For missing fragments in files a `CheckError::Fragment` will be returned
containing a path and the missing fragment.

In Rust documentation non-existent fragments in the form of `#n-m` is
used to highlight a range of lines in the source code. For fragments in
that form additional check is performed to test if all fragments `n`
through `m` exist. In case of missing items in a ranged fragment
`CheckError::Fragment` will be returned containing a path, the
missing ranged fragment, and missing items from the range.

Bare in mind that this introduces overhead of performing n+1 parsing or
fetching via HTTP. This is because multiple links pointing to the same
URL with different fragments end up fetching/parsing the same content
for each fragment. To help with that fragment caching is using
memoization using cached crate.

Fixes #7

CHANGELOG.md

@@ -6,9 +6,11 @@
 
 * If a URL points to a directory, check if index.html exists in that directory. [PR#90]
 * Treat absolute paths as absolute with respect to the `base_url`, not with respect to the file system. [PR#91]
+* Check link fragments, with special handling for Rustdoc ranged fragments to highlight source code lines [PR#94]
 
 [PR#90]: https://github.com/deadlinks/cargo-deadlinks/pull/90
 [PR#91]: https://github.com/deadlinks/cargo-deadlinks/pull/91
+[PR#94]: https://github.com/deadlinks/cargo-deadlinks/pull/94
 
 #### Fixes
 

Cargo.toml

@@ -9,13 +9,16 @@ readme = "README.md"
 license = "MIT OR Apache-2.0"
 
 [dependencies]
+cached = { version = "0.20.0", default-features = false }
 cargo_metadata = "0.9"
 docopt = "1"
 env_logger = "0.8"
 lol_html = "0.2"
 log = "0.4"
 num_cpus = "1.8"
+once_cell = "1.5.1"
 rayon = "1.0"
+regex = { version = "1", default-features = false, features = ["std", "perf"] }
 ureq = { version = "1.5.2", features = ["tls"], default-features = false }
 serde = "1.0"
 serde_derive = "1.0"
@@ -26,3 +29,4 @@ serde_json = "1.0.34"
 [dev-dependencies]
 assert_cmd = "1.0"
 predicates = "1.0.0"
+mockito = "0.28.0"