Merge pull request #2 from Mooophy/master

Update with Mooophy
added 6.1 ~ 6.9
added 6.10
Create Chapter6.h
Create fact.cc
Create factMain.cc
Create ex6_11.cpp
Update README.md
added ex6.10 ~ 6.17
Create ex6_17.cpp
Delete ex6_16_17.cpp
Delete ex6_16_17_18.cpp

Too much code.
added 6.18 ~ 6.22
Create ex6_23.cpp
added 6.23~6.24
Update ex6_25_26.cpp

6.25 said to use string, and we should not print the first argument ( It's the program name )
Update ex6_27.cpp

"sum" is more better name of the function, and the range for loop use "const auto&" more better.
added 6.25 ~ 6.29
rewrite 6.24
added 6.30 ~ 6.35