add --output=[FILE] option to easily override destination
add --output=[FILE] option to easily override destination

Being able to explicitly set the output file helps with debugging,
especially when using scripts to automate tasks. Sure you can set this
by using an --evaluate flag and setting the Lua value manually, but
most people using SILE are not likely to figure that out until much
later in the learning curve than it would have been useful.

neofob/sile,simoncozens/sile,alerque/sile,simoncozens/sile,neofob/sile,alerque/sile,anthrotype/sile,anthrotype/sile,alerque/sile,anthrotype/sile,alerque/sile,simoncozens/sile,neofob/sile,anthrotype/sile,neofob/sile,simoncozens/sile