add draft
add copy constructor
add Return Value Optimization
edit default constructor
add copy-and-swap
add copy assignment
fix punctuation
fix grammatical errors
replace method to func
lecture_12 code indent style improved
lecture_12 stdout text layout improved

actually <br> tags were added to quotes.
add img/double_free
Merge pull request #30 from razykov/add-lecture-12

Add lecture 12