Add extension functions for table assertions.

[ajalt]

These extensions simplify the common case of creating a table and
immediately asserting on its contents. They let you write code like
this:

table(...).forAll { a, b -> ...}

instead of needing an intermediate variable:

val myTable = table(...)
forAll(myTable) { a, b -> ... }

I deliberately did not change any documentation in this PR. If it's
accepted, documentation can be updated in another commit.

[sksamuel]

Excellent!