added 10.11 ~ 10.13 to README

1. refactor 10.11 casue stable_sort should be used after elimdups
2. edit 10.12 that using the class Sales_data of ch07
3. edit 10.13's function name. "longer" better than "bigger"
added 10.14 ~ 10.19 to README

1. added 10.17
2. move 10.14 and 10.15 to README from ex10_14_15_16.cpp
3. rename 10.20.21