fix compatibility with pecl-json-c extension

Squashed commit of the following:

commit e7f2e32806706e02d91e9c23f822c2d4390ea975
Author: Márcio Almada <marcio3w@gmail.com>
Date:   Thu Dec 26 04:07:44 2013 -0300

    added missing require entry for ext-json

commit 7ab3480aa4a489d4e0bc36a7b9d3c30b0e0b1afa
Author: Márcio Almada <marcio3w@gmail.com>
Date:   Thu Dec 26 03:11:33 2013 -0300

    wrapped parseDynamic pecl-json-c related logic into a conditional
    added Parser::useJsoncStrategy method
    closes #20

commit a85a87f7ea4d25ef544514c305c2ae447483b795
Author: Márcio Almada <marcio3w@gmail.com>
Date:   Thu Dec 26 01:39:40 2013 -0300

    fix compatibility with pecl-json-c extension + keeps support for superseded ext/json
    fix #20