Added small section on Unicode
Moving escape sequences back to under Strings

As per advice by Vladimir Smolyar.
Adding reader's email feedback (Dattatray)
Adding mention about MIT OpenCourseWare
Mentioning Kenneth Reitz's Hitchhiker's Guide
Adding more tweets and emails
Mentioning Flask and Django.
Explain bitwise NOT operator with StackOverflow
Mention only Flask.
Mentioning Martyr2's Mega Project List
Adding Python Big Picture link
Adding Future of Python 2 link
Adding links on porting to Python 3
Adding link to complete Serbian translation
Adding Intermediate Projects link
Adding Hidden features of Python link
Adding Reddit discussion on Python tricks link