修正help信息使其与现实相符

[voidint]

NAME:
   tsdump - Database table structure dump tool.

USAGE:
   tsdump [global options] command [command options] [arguments...]

VERSION:
   0.1.0
date: 2017-11-30T22:17:41+08:00
commit: a4ab62cb3842c22f11fd187cf554b6be7dbcdc2f

AUTHOR:
   voidnt <[email protected]>

COMMANDS:
     help, h  Shows a list of commands or help for one command

GLOBAL OPTIONS:
   -H value, --host value      Connect to host. (default: "127.0.0.1")
   -P value, --port value      Port number to use for connection. (default: 3306)
   -u value, --user value      User for login if not current user. (default: "voidint")
   -p value, --password value  Password to use when connecting to server.
   -d value, --db value        Database name.
   -V value, --viewer value    Output viewer. Optional values: txt|md|csv|json (default: "txt")
   -o value, --output value    Write to a file, instead of STDOUT.
   -D, --debug                 Enable debug mode.
   --help, -h                  show help
   --version, -v               print the version

• 调整USAGE。
• 调整VERSION，使内容排列整齐。
• 调整GLOBAL OPTIONS，选项的文字说明内容首字母大小写保持一致。