Adds a `flags` parameter to the request JSON, appearing under the `compile.options` key (alongside such stalwarts as `compiler`, `timeout`, etc.).
This is primarily to support `-file-line-error` as an option, but could have other uses as well.
`flags` should be an array of strings, or absent. If supplied, the listed arguments are added to the base latexmk command.
this avoids problems in the latest version of latexmk where the
$pdflatex variable has been replaced by $xelatex and $lualatex when
running with -xelatex or -lualatex
By default, no timing information will be taken.
On Linux with GNU user land, this value should be configured to `["/usr/bin/time", "-v"]`.
On Mac, gnu-time should be installed and configured to `["/usr/local/bin/gtime", "-v"]`.
