tower-lsp 0.7.0

Added

• Add default implementations to all non-required LanguageServer methods.
• Add support for emitting custom notifications to clients (PR #99).
• Implement support for the following client-to-server messages:
  • textDocument/signatureHelp
  • textDocument/implementation

Changed

• Bump minimum supported Rust version to 1.39.0.
• Convert to std::future and async/await (PR #101).
• Update futures crate from 0.1.28 to 0.3.
• Update lsp-types crate from 0.68.0 to 0.70.
• Update tokio crate from 0.1.12 to 0.2.
• Update tower-service crate from 0.2.0 to 0.3.

Fixed

• Fix some incorrect links in doc comments.