Sections about tools should be reorganized

[alephpiece]

This is related to #7

Section 常用工具 illustrates many useful tools but they might need to be classified to be clearer to users.

Here is my suggestion:

• vtune and cgdb are supposed to be moved to the profiling and debugging sections respectively.
• sysstat, nload, and lm_sensors are monitoring tools, which should be grouped together with zabbix.
• netlogin is frequently used and should be highlighted. @genshen
• cloc is more like something that should be put in your own blogs. @genshen