Go Arg Versions Save

• Argument structs can define Description() and Epilogue(), which are added to the usage string

• Subcommands can have multiple aliases like this:

var args struct {
    Remove *struct{} `arg:"subcommand:remove|rm|r" help:"remove something from somewhere"`
}

• Improves formatting of usage string when the placeholder tag is set to empty string

• Do not handle --version when the args struct lacks a Version() function

• Add StructSubcommands to Config struct

• Correctly brackets non-required positional arguments in usage strings
• Fixes help and usage strings for subcommands.
• Add native support for url.URL via go-scalar
• Add environment variables names to error messages when relevant

This patch release fixes a regression in which unexported embedded structs were mistakenly being ignored.

Minor fix for case where an environment variable containing an empty string is parsed into a slice or map.

• Adds support for parsing into a map (see https://github.com/alexflint/go-arg/pull/149)
• Adds support for options that have no --long version, only a -s short version (see https://github.com/alexflint/go-arg/pull/137)

• Added the placeholder tag
• Improved usage strings when using subcommands
• Improved documentation on using subcommands

This version introduces a new way to specify default values for arguments. The old way still works too.

This version adds support for subcommands. See https://github.com/alexflint/go-arg#subcommands

go-arg has now been stable for ~2 years, so I am releasing version 1.0. This coincides with the migration to the new go module system in #70.