create sane argparse formatter

[techtonik]

Default argparse output is awful. Not total, but a noticeable UX fail.

Compare argparse:

$ vagrant-spk
usage: /usr/local/bin/vagrant-spk [-h] [--work-directory WORK_DIRECTORY]
                                  {setupvm,vm,vm up,vm halt,vm destroy,vm
                                  ssh,init,dev,pack,verify,publish,keygen,getkey,up,reload,halt,destroy,global-status,ssh}
                                  [command_specific_args [command_specific_args ...]]
/usr/local/bin/vagrant-spk: error: too few arguments

With Mercurial:

$ hg
Mercurial Distributed SCM

basic commands:

 add           add the specified files on the next commit
 annotate      show changeset information by line for each file
 clone         make a copy of an existing repository
 commit        commit the specified files or all outstanding changes
 diff          diff repository (or selected files)
 export        dump the header and diffs for one or more changesets
 forget        forget the specified files on the next commit
 init          create a new repository in the given directory
 log           show revision history of entire repository or files
 merge         merge another revision into working directory
 pull          pull changes from the specified source
 push          push changes to the specified destination
 remove        remove the specified files on the next commit
 serve         start stand-alone webserver
 status        show changed files in the working directory
 summary       summarize working directory state
 update        update working directory (or switch revisions)

(use "hg help" for the full list of commands or "hg -v" for details)

With git:

$ git
usage: git [--version] [--help] [-C <path>] [-c name=value]
           [--exec-path[=<path>]] [--html-path] [--man-path] [--info-path]
           [-p | --paginate | --no-pager] [--no-replace-objects] [--bare]
           [--git-dir=<path>] [--work-tree=<path>] [--namespace=<name>]
           <command> [<args>]

These are common Git commands used in various situations:

start a working area (see also: git help tutorial)
   clone      Clone a repository into a new directory
   init       Create an empty Git repository or reinitialize an existing one

work on the current change (see also: git help everyday)
   add        Add file contents to the index
   mv         Move or rename a file, a directory, or a symlink
   reset      Reset current HEAD to the specified state
   rm         Remove files from the working tree and from the index

examine the history and state (see also: git help revisions)
   bisect     Use binary search to find the commit that introduced a bug
   grep       Print lines matching a pattern
   log        Show commit logs
   show       Show various types of objects
   status     Show the working tree status

grow, mark and tweak your common history
   branch     List, create, or delete branches
   checkout   Switch branches or restore working tree files
   commit     Record changes to the repository
   diff       Show changes between commits, commit and working tree, etc
   merge      Join two or more development histories together
   rebase     Forward-port local commits to the updated upstream head
   tag        Create, list, delete or verify a tag object signed with GPG

collaborate (see also: git help workflows)
   fetch      Download objects and refs from another repository
   pull       Fetch from and integrate with another repository or a local branch
   push       Update remote refs along with associated objects

'git help -a' and 'git help -g' list available subcommands and some
concept guides. See 'git help <command>' or 'git help <concept>'
to read about a specific subcommand or concept.