There is a range of different wordings used in the docs of constructor
type functions.
Change all to start with `Constructs a new` or `Constructs an empty`.
In functions that act like constructors there is a mixture of the usage
of `creates` and `constructs`.
Replace all occurrences of `creates` with `constructs` in the first line
of docs of constructor like functions.
This is a straight up move of the whole type because there are only
three methods, a getter, a setter, and `is_signalling_soft_fork`.
If we use an extension trait for `is_signalling_soft_fork` then we
have to make the two private associated consts public which is in my
opinion worse.