Syntax highlighting improvements, debug log, new snippets

• Add debug logging feature. #291
  Run Rust: Open Debug Log command to open the log, used by on-save check and build.
• Add eprint and eprintln snippets. #283
• Some minor word-wrapping fixes. #315
• Syntax: Some where improvements. #303
• Syntax: allow new lines and comments in lambda parameters #307
• Syntax: Support dyn traits. #308
• Syntax: Anonymous lifetimes #319
• Syntax: Support trait definition bounds and type parameters. #320
• Syntax: Support attributes in type parameters. #321
• Syntax: Unreserve reserved keywords. #322
• Syntax: Rework enums #323
• Syntax: Support comments near struct/union. #324
• Syntax: Support *const raw pointer in (some) type positions. #325
• Syntax: Rewrite macro_rules #326
• Syntax: Support never type in type params. #327
• Syntax: Support HRTB in all type positions. #328
• Syntax: Fix unsafe prefix for function types. #329
• Syntax: Fix extern in fn type. #330