[doc] Add sync.cancel documentation.
[doc] Add sync.cancel documentation.

phonegap/phonegap-plugin-contentsync,purplecabbage/phonegap-plugin-contentsync,purplecabbage/phonegap-plugin-contentsync,chrisland/phonegap-plugin-contentsync,phonegap/phonegap-plugin-contentsync,phonegap/phonegap-plugin-contentsync,revolunet/phonegap-plugin-contentsync,revolunet/phonegap-plugin-contentsync,purplecabbage/phonegap-plugin-contentsync,chrisland/phonegap-plugin-contentsync,purplecabbage/phonegap-plugin-contentsync,chrisland/phonegap-plugin-contentsync,revolunet/phonegap-plugin-contentsync,chrisland/phonegap-plugin-contentsync,chrisland/phonegap-plugin-contentsync,purplecabbage/phonegap-plugin-contentsync,revolunet/phonegap-plugin-contentsync,phonegap/phonegap-plugin-contentsync,revolunet/phonegap-plugin-contentsync,phonegap/phonegap-plugin-contentsync,phonegap/phonegap-plugin-contentsync