Option or context manager to change directory

[pawamoy]

Is your feature request related to a problem? Please describe.
I sometimes find myself doing ctx.run("bash -c 'cd dir && actual command'") in order to run a command in another directory.
It's a bit annoying because then it's a shell command and I must quote properly, with the problems that follow.

Describe the solution you'd like
Instead, I'd like to be able to change directory with an option or a context manager:

# with an option
@duty
def task(ctx):
    ctx.run(["actual", "command"], workdir="subfolder")

@duty
def task(ctx):
    with ctx.workdir("subfolder"):
        ctx.run(["actual", "command"])

In fact, we could extrapolate and offer a context manager for all the available options:

@duty
def task(ctx):
    with ctx.options(workdir="subfolder", silent=True):
        ctx.run(["actual", "command"])

Describe alternatives you've considered
The bash -c 'cd && hack.