Merge pull request #8 from massiveart/factory

Introduced replaceable factory service
Added get/set/has field to Document
Added image URL field

Enabled mapping of an ImageUrl field which enables an image URL to
be mapped to the document.
Added Pre-Index event
Added fluent search builder

Enables unintrusive addition of additional contextual parameters such
as locale.
Added deindex method to API
Renamed "go" to "execute". CR fixes.
cleaned code
Merge branch 'added-image-field' into develop
Merge branch 'develop'
updated composer