Use linked list for gadgets chaining
Use arg to get binary filename
Delete Chain_List and format naming conventions
Change Gadget struct to double linked list

 *replace Gadget struct member 'last' to 'prev'
 *prev not only can find last by using head->prev
 *but also can insert nodes more convenient
Update error checking
Check gadget string length boundary
Merge pull request #4 from hwchen18546/develop

Use linked list for gadgets chaining