Break tuples with container in first position

[michalmuskala]

This is still work in progress.

This changes how tuples are laid out when the first element is a complex term - they are printed like lists and other containers. The main use-case for the "flex" tuple layout we used before was to support nicely printing tagged tuples - this is not changed.

Fixes #153

[awalterschulze]

• Tuples inside tuples are no tightly coupled {{A}} with no_break in between, which means tuples inside tuples do not have a weird indentation, see the is_container function
• When the first element in a tuple is not a tag, the tuple is now formatted as if it was a list, see the is_tag function.