pick(path, matcher)(data) : pick values from JSON

``javascript
var person = {
"name" : "John",
"age" : 32,
"kids" : [
{ "name" : "Adam", "age" : 10 },
{ "name" : "Emily", "age" : 7 }
],
"relationships" : [
{ "status" : "ongoing", "with" : { "name" : "Susan" } },
{ "status" : "ended", "with" : { "name" : "Katie" } }
]
};

// ----- path extraction

pick("/")(person) // => person
pick("/name")(person) // => "John"
pick("/kids[0]/name")(person) // => "Adam"
pick("/kids[]/name")(person) // => ["Adam", "Emily"]

// ----- matching

pick("/relationships[*]/with/name", { "/../../status" : "ongoing" })(person)
// => "Susan"

pick("/kids[*]", { "/name" : "Adam" })(person)
// => { "name" : "Adam", "age" : 10 }

`

Idea

* pick(path, matcher)(value) maps value to path and returns the result if matcher accepts it

* path can be thought of as a mapper that maps value as another value selection

* matcher can be thought of as a filter that filters the selection

$3

Paths are defined as /-separated selectors, where each selector maps the current selection
to another value:

| Selector | Maps to | Example
| -------------------- | --------------------- | ----------------------------
| (empty) | current |
| field | current[field] | /name for John maps to "John"
| [idx] | current[idx] | /kids[0]/name for John maps to John's first kid's name, "Adam"
| .. | parent | /../../status (relative to strings "Susan" and "Katie" in the example)

For convenience, field and index-style selectors can be combined in single path segment (i.e. /array[0] instead of /array/[0].

$3

When using [idx] selector, instead of using an numerical index, you can specify a wildcard index using [\*].

This will select the first such value in current selection where the rest of the path can be selected.
I.e. /kids[\*]/name would select "Adam" because "Adam" is the first kid object with a name attribute.

Wildcard matching can be used together with custom matchers to create find-style queries.

$3

You can also omit the index altogether and use [] matcher to filter values in current selection down to those
for which the rest of the path can be selected.

/kids[]/name will thus return an array of ["Adam", "Emily"] because both kid objects contain a name attribute.

Any matching can also be used with custom matchers to create filter`-style queries.