Refactoring developer guide.
Update README.md
Merge pull request #1 from chzyer/patch-2

Update README.md
Refined doc.
Refined doc.
Refined doc.
Refined doc.
Update README.md
Update README.md
Update README.md
Update README.md
Merge pull request #2 from chzyer/patch-3

Update README.md
Refined doc.
Merge pull request #38 from hughlv/develop

Develop