Rationale: this convention avoids forcing closely-related code to be far
apart in the namespace hierarchy, and vice versa. By the same token, it
makes the namespace hierarchy more consistent with the directory
hierarchy.
This library is designed around supporting the kinds of use cases we
expect in the toolchain and other Carbon tools. It supports subcommands,
options, and prints help.
There is still a decent chunk of work to be done to finish polishing
this, but it should give us a solid starting point.
For details about the library and a brief roadmap, see the main comment
in `command_line.h` which provides a comprehensive overview of the
library and a roadmap of the remaining work.
Porting the driver to this went fairly well, but did require some
changes. That port is separated into a follow-up PR #2979.
---------
Co-authored-by: Jon Ross-Perkins <jperkins@google.com>
Co-authored-by: Lucile Rose Nihlen <luci.the.rose@gmail.com>
Co-authored-by: Richard Smith <richard@metafoo.co.uk>
Geoff Romer
