execMaxBuffer option for setting child_process.exec() maxBuffer

[JaroslavMoravec]

319 If engine log a lot of messages to stdout or stderr, the child process is killed. You can increase buffer size by this option.

If you run grunt --verbose, output of fontforge will by logged by logger.

This changes has been made because fontforge produces warning messages if svg format is not fully valid and buffer of stderr can exceed and you should have some way to show these warnings.

[JaroslavMoravec]

Default value for execMaxBuffer is same as in https://nodejs.org/api/child_process.html#child_process_child_process_exec_command_options_callback I didn't find how to get this value from child_process object.

[sapegin]

Cool, thanks!

[JaroslavMoravec]

Cool, thanks too.

[sapegin]

Out in 1.2.0, thanks!