The user `~/.ssh` config forwarding is now controlled by the
`CQFD_NO_USER_SSH_CONFIG` environment variable. This allows finer
control over the ssh configuration forwarding.

When running commands that use git, it is useful to have the user's
.gitconfig available in the container. Mostly to have the user's name
and email configured.

For instance, when running Yocto's `devtool modify`, it will produce
an error if the user's name and email are not configured.

I chose to enable this new option by default, but it can be disabled
with the `CQFD_NO_USER_GIT_CONFIG` environment variable. It is
documented in the README.

When running `cqfd run -c` commands, the default login shell could be
used instead of the one defined for `cqfd shell`. This was confusing
and not configurable. The same shell will be always used, defined by
the `CQFD_SHELL` environment variable.

This notably overcomes a regression when using scripts that require
bashisms. In the previous release, the default shell was `/bin/bash`,
and is now `/bin/sh`. Users relying on bashisms still need to set
`CQFD_SHELL` to `/bin/bash` in their environment.

See issue #310.

The default shell used to be /bin/bash. This was changed to /bin/sh
arbitrarily in commit 0051142 which broke builds for users relying
on bash-specific features. Notably running bitbake.

See Issue #130

It can be useful for users to get access to the docker commands in
order to tweak them, or dissect the options passed.

When running bash-completion's completion functions in zsh, the
`_init_completion` and `_get_first_arg` functions are not defined in
`bashcompinit`. Defining dummy functions allow using auto-completion
in zsh although its not as accurate.

Without _get_first_arg, the completion doesn't detail the options
specific to that command and lists all of them.