Max file size

[rogelio-o]

The max size of the incoming request of AWS lambda is 6Mb, but maybe we will require little size for our incoming files.

The goal of this issue is allow to configure the max size of the incoming files in the MultipartParser. It will exist a parameter in the options passed to the parser that will indicate the max size. In case that a file of the multipart form would be bigger than the max size, an error has to be thrown.