Add Coodinate system
Chapter 6 resources
Modify Coordinate systems
Update 2.md

Fixing typo.
Update the "Why choose" list

This is a start. 

Need more things. I would like to see a list for the vast API included in the last bullet point. I don't know the complete list. Maybe: sprite (atlas, sheet), actions, animations (including skeletal), particles, transitions, timers, events (touch, keyboard, accelerometer, mouse), sound, file IO, persistence
Added a list of examples for the vast API available

This list needs to be updated.
Merge pull request #16 from kr15to/patch-1

Thank You
Merge pull request #17 from kidproquo/master

Make the why choose list more comprehensive
Add content for chapter 11 about `call custom c++ from lua` and `bind a c++ class to lua automatically`
Merge pull request #14 from RaoZiJian/master

Add Coordinate Systems in Chapter 6
Merge branch 'master' of https://github.com/chukong/programmers-guide
Merge pull request #18 from samuele3hu/master

Add content for chapter 11 about `call custom c++ from lua` and `bind a c++ class to lua automatically`
conventions section
typos
conventions section
modify indentation
modify format
fix indentation problems
adjust text format
add more describe to the new ui label