Semi-stable early alpha Gcodehost branch for ESP3D 3.0

Currently only confirmed to work for Marlin

Works fairly well, but prints stop momentarily (2-3s) when new connections are made. (such as when refreshing the browser)

to start print:

[ESP700]File-to-print.gcode
[ESP700]SD/File-to-print.gcode
[ESP700]foldercontainingfile/File-to-print.gcode
[ESP700]SD/foldercontainingfile/File-to-print.gcode

print commands:

[ESP701]action=abort
[ESP701]action=pause
[ESP701]action=resume

Pause/Resume/Abort/startup script paths are specified in configuration.h, from "ESP_AUTOSTART_SCRIPT_FILE" onwards. (set as the path to a gcode file containing the assosciated script)

The ESP3D Configurator can be used by replacing the line #define GCODE_HOST_FEATURE in configuration.h with the following block, where the paths are scripts containing the commands to be executed upon their assosciated function. Comment them out as required if unused.

#define GCODE_HOST_FEATURE

#if defined (GCODE_HOST_FEATURE)
#define ESP_HOST_TIMEOUT 30000
#define ESP_HOST_BUSY_TIMEOUT 5000
#define MAX_TRY_2_SEND 5

#define HOST_PAUSE_SCRIPT "SD/Scripts/Pause.gco"
#define HOST_RESUME_SCRIPT "SD/Scripts/Resume.gco"
#define HOST_ABORT_SCRIPT "SD/Scripts/Abort.gco"
#endif //GCODE_HOST_FEATURE