Create learning_and_evaluation.py

A Learning Framework includes several learning algorithms and their comparison through evaluation of performance metric. 

#Features
	Length
	Sentiment
	Thread line
	Relative thread line number
	tf-idf sum
	tf-idf average
	email number
	relative email number
	reply number
	recipients number

#Learning methods:
1. Logistic Regression
2. Naive Bayesian Network
3. SVM

# Evaluation Metrics
1. AUC
2. F1 Score
3. Accuracy
4. Precision
5. Recall