Makes it optional whether to indent arms in match expressions. Setting this
to false may be desirable for people wishing to avoid double-indents, in
that if the match arm is a block, the block will cause an extra indentation
level, and if it isn't a block but just a single line, it's still easy to
see the logic at a glance.
This style is preferred in certain other languages with switch statements,
e.g. Linux style C and the most common Java style.
