v0.4.0

[tony-iqlusion]

• Update dependencies: gumdrop 0.7, secrecy 0.4 (Update dependencies: gumdrop 0.7, secrecy 0.4 #141)
• template: Lint for 2018 edition idioms; export error macros (cli/template: Lint for 2018 edition idioms; export error macros #136)
• Improve lints and deny policy (Improve lints and deny policy #135)
• derive: Update to 1.0 versions of proc-macro2/quote/syn (derive: Update to 1.0 versions of proc-macro2/quote/syn #134)
• Support positional arguments in usage descriptions (Support positional arguments in usage descriptions #131)
• Fix issues with the signal handler thread (Fix issues with the signal handler thread #130)
• template: Add Deref impl on Error newtype (template: Add Deref impl on Error newtype #129)