added workaround to load Request body only if needed 

On every call routed by flightphp, the Request body will be read by the Request object (even if it is not used at all). This is very time (CPU cycles) and memory consuming if you use file upload or PUT requests as the whole data get loaded into memory in one chunk.

Additional it is possible to crash the whole php application by only sending enough data as the request could not be parsed anymore.

Added workaround to load body only if it's needed (and not loaded by the application itself).