Returns the first param value with the given name from the given params.
Returns undefined if no param value with that name is set.
If the name denotes an array field (e.g. foo[]), all param values with the given name
are returned as an array. If no param value with that array name is set, an empty
array is returned.
To always return a single value use up.Params#getFirst() instead.
To always return an array of values use up.Params#getAll() instead.
Example
var params = new up.Params({ foo: 'fooValue', bar: 'barValue' })
var params = new up.Params([
{ name: 'foo', value: 'fooValue' }
{ name: 'bar[]', value: 'barValue1' }
{ name: 'bar[]', value: 'barValue2' })
]})
var foo = params.get('foo')
// foo is now 'fooValue'
var bar = params.get('bar')
// bar is now ['barValue1', 'barValue2']
