Search `docstring` for backticks and attempt to link those functions to respective documentation.

def link_docstring(modules, docstring:str, overwrite:bool=False)->str:
    "Search `docstring` for backticks and attempt to link those functions to respective documentation."
    mods = listify(modules)
    for mod in mods: _modvars.update(mod.__dict__) # concat all module definitions
    return re.sub(BT_REGEX, replace_link, docstring)