Make the Python interpreter easier to configure

Python is a bit dependant on the installation/distribution. For example
in older Ubuntus, python2.7 is not the default. Other distributions
don't use the version in the binary. To overcome these problems there
was an incomplete support to install the command to use a particular
python binary, but this didn't work if the "building" environment wasn't
using python 2.7 as the default Python interpreter.

This commit is intended to fix this, by using `make PYTHON=mypython`.
Use fpm to create the debian package

Using the regular debian infrastructure to create the packages is very
overwhelming. Also, one debian directory should be used for each
debian/ubuntu distribution, which is way out of the scope of this tool.

If at some point a serious debian/ubuntu packages wants to make proper
packages, he/she can do so in an external repository, this is how
normally debian packaging works.

To do this some stuff about version numbers and released had to be
adjusted too.
Fix unrelated phrase in the man

Fixes #70.
Fix help message for issue comment argument
Fix issue/pull request help messages

The variable used to change the name of the object being described was
completely wrong, because it was a class object so it never varied. When
possible, now `cls` is used instead, and when is not the object name is
just specified manually.

A few help typos are also fixed.
Add git_dir() function to get the .git directory
pull rebase: Add --stash-(include-untracked|all) options

To address #22 in a simple way, the new options --stash-all and
--stash-include-untracked were added to the pull rebase command, which
translate directly into --all and --include-untracked when invoking the
git stash command.

Previously --all was always used, and caused a lot of trouble with
repositories storing big data files that were outside git control. Now
the default is changed to do a plain git stash, at the expense of
slightly bigger probabilities of getting some conflict in the checkout
of the pull request when rebasing. So to keep using the safe option, now
is necessary to pass --stash-all explicitly.
Fix listing issues for repos without issues

Fixes #79.
Allow partial parsing of arguments

This is a move towards implementing #69. Basically if setup_parser()
returns true, parse_known_args() will be used instead of the regular
parse_args() and any unknown argument will be placed in
args.unknown_args.
Allow commands to override the usage string

This is another move towards implementing #69. If a command class
defines the attribute `cmd_usage`, then it will be used as the usage
string for that particular command.
clone: Forward unknown options to `git clone`

This allows passing any arbitrary option to git clone when cloning
a GitHub repository.

Fixes #69.
Use GitHub media type v3

GitHub is changing the default media type used soon. The changes
compared to the current default (beta) are minimum and this tool
shouldn't be affected. Just to make sure we are using a fixed version
(which now is the latest), we explicitly ask for the
"application/vnd.github.v3+json" media type now.

For more details see:
https://developer.github.com/changes/2014-01-07-upcoming-change-to-default-media-type/
Set architecture to all in the Debian package
README: Add fpm to the dependencies

Fixes #81.
clone: Add --triangular workflow option

This options makes pushing to the fork and pulling from the upstream
repo by default. Please read the man page for details.

Fixes #64.
Added `git hub issue show -f <n>`

This command is for listing more information on one issue or several.
Renamed methods for printing an issue

old print_issue() is now print_issue_summary().
old print_issue_completely() is now print_issue().

As proposed in #76.
Shortened printing full issue information

This patch changes the printing of the full issue information by
composing a list of labels by joining the labels into a new field inside
`issue` and using this one.
Added issue comments printing

This patch adds the printing of the comments of the issue(s).
always print the full information on an issue, as proposed in #76