- include 'struct fs_file' in 'struct http_state' to prevent file allocation fails when connection allocation succeeded (plus have less allocations/pools);
- added (conditional) code to abort the oldest connection when allocating a new connection fails;
- fixed some warnings;
- added delayed open/read functionality (so that SSI code can delay sending of a file until internal data is available);
- clean up fs-handling: additional read is not required with our current fs implementation;
- kill oldest connection when running out of http_state memory;
- splitted SSI state into its own struct so that non-SSI pages don't consume too much memory (SSI buffer can get quit big);
- added support for HTTP/1.1 persistent connections (use the '-11' switch of makefsdata; not available for SSI files since we cannot calculate the file length in advance);
- splitted the unreadably-long function http_send_data into multiple smaller functions;
- http_close_conn must handle hs==NULL correctly (when called from http_poll);
- added LWIP_HTTPD_ABORT_ON_CLOSE_MEM_ERROR to call tcp_abort when tcp_close fails with out-of-memory error;
- httpd_init checks if the memp pool MEMP_HTTPD_STATE is big enough if HTTPD_USE_MEM_POOL==1
- fixed copy/nocopy for SSI files;
- added LWIP_HTTPD_SSI_MULTIPART (default off): when on, SSI functions have one more argument that is used as state for an SSI tag to return more than LWIP_HTTPD_MAX_TAG_INSERT_LEN bytes (the handler function is then called multiple times);
- added LWIP_HTTPD_POST_MANUAL_WND (default off): when on, post callbacks can throttle RX speed by manually sending window updates (i.e. tcp_recved is called manually by calling httpd_post_data_recved);
- added LWIP_HTTPD_FILE_STATE (default off): when on, fs_open/fs_close call application defined functions fs_state_init/fs_state_free (fs_state_init returns a void pointer that is passed to every call to an SSI handler);
- compacted the code a bit by moving the code that calls tcp_write() in a loop to its own function;
- error files may have the extension shtml, too;
- fixed that returning default 404 page did not work any more;
