Add startswith and friends as methods on memoryview

[Daverball (David Salvisberg)]

You may also be interested in this recent discussion that came up in the context of PEP 467 which proposed more types of view objects and/or better interpreter level support for zero-copy slice operations:

More kinds of view objects in the standard library to enable zero copy slicing

Big +1 for this, especially if we can also have a writeable strview backed by e.g. a io.StringIO object. It always kind of irked me how wasteful str is for simple slicing operations (or concat in the writeable case, although StringIO is a decent solution there, but the API for a strview could be a bit more ergonomic compared to StringIO, since you’d likely want strview to be fully compatible with str, i.e. everywhere that accepts a str can also take a strview without any surprises, so things li…