Create KeySet rule

[henriquemoody]

• v::keySet(Key $rule...)

Validates a keys in a defined structure.

$dict = array('foo' => 42);

v::keySet(
    v::key('foo', v::int())
)->validate($dict); //true

Extra keys are not allowed:

$dict = array('foo' => 42, 'bar' => 'String');

v::keySet(
    v::key('foo', v::int())
)->validate($dict); //false

Missing required keys are not allowed:

$dict = array('foo' => 42, 'bar' => 'String');

v::keySet(
    v::key('foo', v::int()),
    v::key('bar', v::string()),
    v::key('baz', v::bool())
)->validate($dict); //false

Missing non-required keys are allowed:

$dict = array('foo' => 42, 'bar' => 'String');

v::keySet(
    v::key('foo', v::int()),
    v::key('bar', v::string()),
    v::key('baz', v::bool(), false)
)->validate($dict); //true

The keys' order is not considered in the validation.

Fix #350

[alganet]

I like it!

[vikyd]

Can Extra keys are not allowed optional ?
I have many params in my $_POST, I will only use some of them.

[henriquemoody]

Then just use a chain of key() rules, @Viky-zhang :)

KeySet exists only to validate structures, or else, just use nested key().