add description; misspell translator to translater
2～3 paragraph
modified some details.
Merge branch 'zh-Hans' of https://github.com/rickytan/articles into zh-Hans
littel change
Update 2012-09-17-nscharacterset.md
Merge pull request #118 from rickytan/zh-Hans

Modified some of the CGGeometry; added more of NSCharacterSet