Toggle

A Toggle stores state for Terminal effects that involve turning on some state within a block of code and turning it off when that block exits. A typical example is text styling: we have a block where we want invert styling enabled, and when the block finishes we want inverted styling turned off. A complication arises when we can nest blocks. An inverted block might be nested inside another inverted block. It's only when the outer block exits that the styling should be turned off. A Toggle handles this with a counter. Only when the counter hits zero do we emit the reset escape code.