FR: syntax highlighting for Fortran

[iahung2]

It seems Lite XL doesn't have it, too:

https://github.com/lite-xl/lite-xl/tree/master/data/plugins

https://github.com/lite-xl/lite-xl-plugins/tree/master/plugins

(there is no language_fortran.lua)

Scintillua does have support for Fortran:

https://github.com/orbitalquark/scintillua/blob/default/lexers/fortran.lua

[Martín Lucas Golini]

Added, direct conversion from lite-xl plugin.