Fix feature interop with examples

.travis.yml

@@ -12,4 +12,5 @@ script:
   - cargo run --example arena
   - cargo run --example mutable_arena
   - cargo run --example sync
+  - cargo run --example string_interner --features indexmap
 

Cargo.toml

@@ -13,3 +13,11 @@ categories = ["data-structures", "caching"]
 [dependencies]
 stable_deref_trait = "1.1.1"
 indexmap = { version = "1.6", optional = true }
+
+[package.metadata.docs.rs]
+features = ["indexmap"]
+
+[[example]]
+name = "string_interner"
+path = "examples/string_interner.rs"
+required-features = ["indexmap"]

README.md

@@ -9,3 +9,9 @@ This crate provides various "frozen" collections.
 These are append-only collections where references to entries can be held on to even across insertions. This is safe because these collections only support storing data that's present behind some indirection -- i.e. `String`, `Vec<T>`, `Box<T>`, etc, and they only yield references to the data behind the allocation (`&str`, `&[T]`, and `&T` respectively)
 
 The typical use case is having a global cache of strings or other data which the rest of the program borrows from.
+
+### Running all examples
+
+```bash
+cargo test --examples --features indexmap
+```