We prevent LaTeX from reading/writing files in parent directories;
additionally, we have introduced a list of unsupported commands which
the user will be informed on if they attempt to use any, so that they
receive a friendly error message instead of LaTeX likely encountering
an error. Finally, we have resturctured the command definitions to
use methods and multi-line blocks, for readability.
Rewrote much of the application to use Promises instead of callbacks.
Replaced the two previous image conversion packages with Sharp, which now
handles svg-to-png and svg-to-jpg conversion. Added queueing support to
prevent resource exhaustion.
