Change argument processing to allow prompt or file args.

[Tindell]

To implement this, I first changed how the prompt and file args are processed, so that they turn off the default interactive mode and color. Then I added the provided prompt into embd_inp after the instruction and prompt prefix.

I also moved some default configuration settings into utils.h to be consistent with llama.cpp.

For example, you can run:
./chat -p "write a python script that prints the current time" or chat -f prompt.txt
to make it print just the response to that prompt. Or:
./chat -p "write a python script that prints the current time" --interactive
To respond to the first prompt and then continue interactively.

See issues 68 and 95.