Function: copy_file

--Usage--
> copy_file(filename)

Copy a file from the export template package to the output directory.
If a file with the given name already exists it is overwritten.

Returns the name of the file written.

This function can only be used in an [[type:export template]], when <tt>create directory</tt> is true.

--Parameters--
! Parameter	Type			Description
| @input@	[[type:filename]]	File to copy

--Examples--
> copy_file("logo.png") == "logo.png" # this file is now in the output directory

--See also--
| [[fun:write_text_file]]	Write a text file to the output directory.
| [[fun:write_image_file]]	Write an image file to the output directory.