[Feature Request] Support changing the locale in a initiated Faker instance.

If I wanted to access the italian locale instead of the english US locale, I would have to re-initiate or create a new instance of Faker by passing it_IT as the locale parameter.

f = Faker('en_US')
print(f.name())

f = Faker('it_IT')
print(f.name())

But why not we just do:

f = Faker('en_US')
print(f.name())
f.set_locale('it_IT)
print(f.name())

It's just convenient I believe.