afFieldValueContains: -values, +value as function

proposed "values" - it is bad way, you can see my attempts [here](https://github.com/aldeed/meteor-autoform/pull/515)

very simple and true solution:
```
<template="myForm">
...
  {{#if afFieldValueContains name="myField" value=conditions}}
...
</template>
```
```
Template.myForm.helpers
  "conditions": ->
    (currentValue) ->
      currentValue # you can place your conditions here 
```