v0.34.0

This major version greatly simplifies the parsing of command-line arguments by
marcel scripts.
First, you can use a "shebang" to run a marcel script, e.g.

#!/usr/local/bin/marcel

Next, suppose you want to write a script, filestats, to do the following:

• Find all the files either immediately inside a directory, or inside the directory recursively.

• Optionally, filter the files by extension (e.g. py to find all python source files).

• Count the files and find the total size of those files.

So the script has some optional arguments:

• -r or --recursive to specify whether you want recursion.

• -e or --ext to specify the extension of interest.

• An argument to specify a directory. If omitted, the current directory is used.

So to find the count and size of all files in the current directory:

filestats

To find the count and size of all jpg files recursively under /foo/bar:

filestats -r -e jpg /foo/bar

or equivalently:

filestats --recursive --ext jpg /foo/bar

Command-line parsing is donw as follow.

(parse_args(ext=flag('-e', '--ext'), \
            recursive=boolean_flag('-r', '--recursive'), \
            dir=anon()))

• parse_args is the function that parses the command line arguments.

• It assigns three environment variables, ext, recursive, and dir.
  The command line arguments will be parsed and assigned to these variables for use later in the marcel script.

• ext=flag('-e', '--ext'): This says that the value following a command-line flag -e or
  --ext will be assigned to the environment variable ext.

• recursive=boolean_flag('-r', '--recursive'): This says that -r
  or --recursive is a boolean flag. No value is specified.
  The value of the environment variable recursive will be True if -r
  or --recursive is specified, False otherwise.

• dir=anon(): This says all other command-line arguments (i.e., not flagged)
  will be assigned to the environment variable dir.

• In addition, the unparsed command line will be assigned to the environment variable ARGV.

So if your command line is:

filestats --recursive --ext jpg /foo/bar

then these environment variables are set:

• recursive: True
• ext: "jpg"
• dir: "/foo/bar"
• ARGV: ["filestats", "--recursive", "--ext", "jpg", "/foo/bar"]