DynArray interface documentation

[UnixJunkie]

since tags are missing for many new functions

[UnixJunkie]

the interface is probably not synchronized with the implementation regarding the type of exception thrown in each case

[UnixJunkie]

@andrep @fccm

[fccm]

Half of the functions from this module raise Pervasives.Invalid_arg, and the others DynArray.Invalid_arg.
Maybe we could uniformise it.
Then which one would you prefer to keep?

[UnixJunkie]

The problem is that this is a breaking change.
Old functions which were already throwing an exception should not have its type changed.
If recently introduced functions introduced Pervasives.invalid_arg, it would be better if we stick to the exception
that was already present in the module (DynArray.Invalid_arg).

[UnixJunkie]

thanks to @fccm