Support sending large data sets

[Mihael Schmidt]

The send procedure only supports 65536 bytes of data to be sent. For some cases this might not suffice.

The idea is to split the whole process of sending the data into three steps:

1. add header to send buffer
2. add data to buffer
3. signal finish

The procedure for the second step may be invoked several times.

The third step just sets the connection flag.

droplet_service_setFlag(connection : MONGOOSE_FLAG_SEND_AND_CLOSE);

[Mihael Schmidt]

This should be implemented using chunked data transfer, see https://docs.cesanta.com/mongoose/master/#/c-api/http_server.h/mg_send_http_chunk.md/ .

[Mihael Schmidt]

added support for large data sets, resolved issue #21

• added mongoose prototypes for chunked data
• added procedures for sending header and chunked data

→ <<cset 179aed3ecf9f>>