Support reading multiple files from a single .f file

[ShashankVM]

A feature request to add support to read all source files from a .f

How it works:

1. Specify list of source files in a .f file.
2. Read the .f file using ebmc -f filename.f

Why do we need it?

1. Currently the -I does not work. Created a separate issue for that: -I option not working as intended in EBMC #1338
2. It will be easier to read files and have a shorter run command when the project has a lot of files.
3. .f is a method used by multiple EDA tools, this reduces effort in adopting EBMC.

Reference:

-f <filename>
(command argument file)	Instructs Verilog-XL to read the text file that you specify following the option. The text file can contain source text filenames and Verilog-XL command options, including other -f options. Nesting is virtually unlimited, but a maximum of 1024 characters has been set to trap recursive -f options.

Source:
https://portal.cs.umbc.edu/help/VHDL/verilog/command_line_options.html