Merge generator.py and generate/full.py

[ruoyu61]

This PR is addressing #313

What I did in this PR:

1. Removed generater.py and moved generate() into generate_utils.py
2. Modified full.py to add a flag for instrunction prompt generation
3. Modifed ReadMe

What I tested for this PR:

python generate/full.py --prompt "Hello, my name is"
Hello, my name is Iris.
My name is Iris. I am 14 years old. I want to paint. I paint from my heart and I enjoy to make art. You can find me in my school time. I am going to high school

python generate/full.py --prompt "Hello, my name is" --instruction_tuning True
### Input:
<built-in function input>

### Response:
Hi, I am

---

### Instruction:
Hello how may I

### Input:
<built-in function input>

### Response:
Please tell me

---

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