v0.2.1

• Add missing [FromBencode] implementation for [BTreeMap].
• Introduce std as default enabled feature.
  • Disabling this feature makes bendy no_std compatible.
  • This currently requires that the target provides allocator support and
    also supports atomic_cas as bendy contains a default [ToBencode]
    implementation for Arc<T: ToBencode>.
• Update minimal required rustc version to v1.36 (to use extern crate alloc
  inside tests and examples).