Remove the unused $FORMAT variable

The original idea was that $FORMAT would help determine the type of
output to create.  However, $FORMAT_URL serves that purpose.  We also
update the comments to that they describe the values of $FORMAT_URL.
Stop requesting the beta version of GitHub’s JSON media type

The documentation at

    http://developer.github.com/v3/media/

explains the various media types which GitHub accepts.  We start using
the ‘application/vnd.github+json’ media type because GitHub is
planning to drop the beta versions sometime this year.  Our new media
type will always give us data in the latest format.  In the future we
may need to specify an API version but for the sake of future changes
we will structure the program around newest JSON data available.
README: Explain how to generate the man page

This patch also removes a couple of items from the ‘Upcoming Features’
list since they are now part of the program.
Allow showing the owner of each fork

This patch adds two new command-line options: ‘-n’ and ‘--name’.
Providing either one of these options makes the program display a
username next to each URL showing who owns that fork.  We want the URL
and name to appear on the same line for use with ‘read’ in the future,
which means we have to use the ‘@text’ directive in our JSON query.
This lets avoid the newline, but requires we wrap all parts of the URL
in parentheses.

Implementing the feature demonstrated a problem with the while-loop
that processes the command-line options: the program would not always
read all options.  This patch corrects that behavior.
README: Add an example using the program to add remote repositories
Implement the ‘-s’ and ‘--sort’ options for sorting forks

This option accepts the sorting values that the GitHub API accepts
when listing forks, documented at:

    http://developer.github.com/v3/repos/forks/

Currently we only accept values that we can pass directly to GitHub’s
own API.  It is technically possible for us to perform further sorting
based on values in the JSON data we receive; we can use the ‘jq’
program to perform such sorts.  But this patch does not attempt to add
that behavior, instead saving it as a feature to implement later.
Save the response from GitHub in a temporary file

This patch makes the program create a temporary file via ‘mktemp’,
which we document as a requirement.  Inside of that file we store a
copy of everything we receive from GitHub’s API, i.e. everything the
file has a copy of everything the ‘jq’ program receives.  We intend to
use this for debugging purposes only and therefore we do not tell the
user about the file.  Developers who need to debug the program and
want to examine that data can browse to the directory with the
temporary files and sort them by the most recent modification time.
README: Remove mention of sorting options now that they are available

We still can and should improve the ways users can sort the list of
forks but for now ‘--sort’ functions well enough.
Show the output filename when given the ‘--verbose’ option

The program always creates a temporary file containing all of the
output from GitHub.  This new option displays the name of that file to
help ease debugging by making it clear what file contains the data for
the most recent invocation.
Remove misuse of double-colons in the option definitions

Using a double-colon with getopt indicates that an option accepts an
optional argument.  The definitions for ‘--help’ and ‘--verbose’
incorrectly use the double-colon.  They accept no arguments.
Providing optional arguments to them causes no errors, but it is
semantically incorrect.  So this patch corrects the option definitions
to make it clear that neither ‘--help’ nor ‘--verbose’ accept any
command-line arguments.
Honor HTTP redirections from GitHub

The API documentation at

    http://developer.github.com/v3/#http-redirects

describes how GitHub may redirect a request by returning a 301, 302,
or 307 HTTP response code.  This patch tells cURL to honor those and
resend the request to the new location automatically.
README: Remove the entire ‘Upcoming Features’ section

Version 1.0.0 is close to completion and so I feel like there is no
serious reason to keep this information in the README anymore.
README: Improve the notes about creating the manual

First this patch removes mention of the ‘--help’ option since Git
shows information about the alias, and not the script, when we try to
invoke it via that alias.  Second, this patch shows the Pandoc command
that will create the man page if the user does not have Tup installed
to perform that task automatically.
Remove ‘-h’ and ‘-v’, and replace ‘--help’ with ‘--usage’

We get rid of the short-hand notations for displaying help and version
information because we may want to use those for something else in the
future, e.g. ‘-v’ as short-hand for ‘--verbose’.

Running this program via an alias results in Git showing the alias
definition when given the ‘--help’ option.  This patch replaces that
option with ‘--usage’ to avoid that conflict.
Implement the ‘--rate-limit’ option

GitHub allows a fixed number of API requests per hour and each time we
run the program to list forks we are using up one of those requests.
This patch adds an option which will display the remaining number of
times we can use GitHub’s API along with the date and time when GitHub
will reset our amount of allowed requests.  Using this option takes
precedence over everything else and will stop the program from
listing any forks.  However, using ‘--rate-limit’ will not count
against the number of allowed API requests.