Release v2.2.1

Changes since last release:

• Make client-side error alerts slightly more clear.

Release v2.2.0

Changes since last release:

• Bump github.com/spf13/viper module from v1.7.0 to v1.7.1.
• Bump github.com/spf13/cobra module from v1.0.0 to v1.1.3.
• Migrate to new go:embed feature in Go version 1.16.
• Update module checksums.
• Update and copyedit text in README and Postal queue alert template.
• Change template file extensions to .mustache.

Release v2.1.0

Changes since last release:

• Refactor code that deals with client-side logging.
• Improve HTTP compliance of server command.
• Refactor server-side HTTP code to use the github.com/gorilla/mux package.
• Include software version in the client's User-Agent header.
• Set Cache-Control header on server to prevent caching.
• Add server-side error handler.

Release v2.0.0

Changes since last release:

• Reword alert templates.
• Preserve trailing whitespace in alert templates.
• Initialise Go modules.
• Include version info in build.
• Switch to Cobra for flag parsing.
• Switch to Viper for config parsing.