Modules: introduced js_shared_dict_zone directive.

Modules: introduced js_shared_dict_zone directive.

The directive allows to declare a dictionary that is shared among the
working processes. A dictionary expects strings as keys. It stores
string or number as values. The value type is declared using
type= argument of the directive. The default type is string.

example.conf:
    # Declares a shared dictionary of strings of size 1 Mb that
    # removes key-value after 60 seconds of inactivity.
    js_shared_dict_zone zone=foo:1M timeout=60s;

    # Declares a shared dictionary of strings of size 512Kb that
    # forcibly remove oldest key-value pairs when memory is not enough.
    js_shared_dict_zone zone=bar:512K timeout=30s evict;

    # Declares a permanent number shared dictionary of size 32Kb.
    js_shared_dict_zone zone=num:32k type=number;

example.js:
    function get(r) {
        r.return(200, ngx.shared.foo.get(r.args.key));
    }

    function set(r) {
        r.return(200, ngx.shared.foo.set(r.args.key, r.args.value));
    }

    function delete(r) {
        r.return(200, ngx.shared.bar.delete(r.args.key));
    }

    function increment(r) {
        r.return(200, ngx.shared.num.incr(r.args.key, 2));
    }

In collaboration with Artem S. Povalyukhin, Jakub Jirutka and
洪志道 (Hong Zhi Dao).

This closes #437 issue on Github.