Add support for debugging .robot files

[jasle]

Currently it is possible to set breakpoints inside python code but not in .robot-files.

It would be great to have also the possible to use the debugger with them.

[tiodot]

老哥有空支持一下这个功能么 @jnhyperion

[jnhyperion]

这个功能比较复杂，不是一时半会可以实现的。This is a complex feature which requires many efforts, unfortunately I still do not have enough time working on this.

[jnhyperion]

Using python file debugging will solve most of our usually cases:

kw.py

def my_debug(arg):
    print(arg) # add break point here

*** Settings ***
Library    kw.py
*** Test Cases ***
my test
     foo
     my debug    ${var_you_want_to_debug}     # add py kw here
     bar