Refactor s:job_start()

Add stdout/stderr event handler for debugging

Add two options to disable ctags/gtags support jsfaint#6

Fix callback function issue.

Update README.md

A better solution for jsfaint#4

Add two functions to wrap command execution.

ClearGTAGS: run cscope kill before delete GTAGS files.

Modify output message.

Update README.md

Add hotkey for cscope, obsolete cscope_macros.vim

Modify README.md