Verilog HDL support for Visual Studio code

Try to implement a language server for verilog HDL.

• 2019/7/14 Add port list for auto-completion.
• 2019/7/11 Code refactoring.
• 2019/7/8 Add module name for auto-completion.
• Use textEdit for autocompletion.
• Fixed keyword detail description issue.
• Add keywords for auto-completion.