Improved read_line() performance
Improved s:system() timeout
Clean-up interrupted process
Improve documentation.

Write:

1. File object
1. Socket object
1. Process object
Merge pull request #163 from Shougo/improve-system

Improve s:system()
Merge pull request #162 from Shougo/improve-read_line

Improve read_line() performance
Merge pull request #164 from kamichidu/pr

Improve documentation.