Remove unnecessary assertions
Don't try to serialize `<input type=file>`
Add test that `<input type=file>` won't be serialized
Fix serializing `<select multiple>` values
Add test that `<select multiple>` will properly be serialized
Simplify `serializeArray()` implementation
Fix `serializeArray()` on empty collections
Name the form field variable inside the loop

Instead of repeated access to `this` and prematurely wrapping the field
element in a Zepto collection, name `field` as a variable and use
properties to access attributes instead of with `attr()`.
Merge branch 'form-serialize'

Fixes #1010, closes #1012
Fixes #1011, closes #1013
Fix preventing form submits with `submit(false)`

Check whether `callback` argument was passed, not its value.