Add option to debug with command-line arguments. (leoluz#15)

This commit introduces a new option called:

   Debug (Arguments)

When selected, the user will be prompted to enter
any command line arguments to provide to the program
being debugged.

The initial implementation is naive in that it splits
the input string using the space character (" ") as
the separator.

README.md

@@ -49,6 +49,16 @@ To debug the closest method above the cursor use you can run:
 
 It is better to define a mapping to invoke this command. See the mapping section bellow.
 
+### Debugging with command-line arguments
+
+1. Select the option `Debug (Arguments)`
+1. Enter each argument separated by a space (i.e. `option1 option2 option3`)
+1. Press enter
+
+![Start Debug Session with Arguments](./images/image1.png "Start Debug Session with Arguments")
+![Enter Arguments](./images/image2.png "Enter Arguments")
+![Begin Debugging](./images/image3.png "Being Debugging")
+
 ## Mappings
 
 ```vimL

lua/dap-go.lua

@@ -29,6 +29,25 @@ local function load_module(module_name)
   return module
 end
 
+local function get_arguments()
+  local co = coroutine.running()
+  if co then
+    return coroutine.create(function()
+      local args = {}
+      vim.ui.input({ prompt = 'Args: ' }, function(input)
+        args = vim.split(input or "", " ")
+      end)
+      coroutine.resume(co, args)
+    end)
+  else
+    local args = {}
+    vim.ui.input({ prompt = 'Args: ' }, function(input)
+      args = vim.split(input or "", " ")
+    end)
+    return args
+  end
+end
+
 local function setup_go_adapter(dap)
   dap.adapters.go = function(callback, config)
     local stdout = vim.loop.new_pipe(false)
@@ -75,6 +94,13 @@ local function setup_go_configuration(dap)
       request = "launch",
       program = "${file}",
     },
+    {
+      type = "go",
+      name = "Debug (Arguments)",
+      request = "launch",
+      program = "${file}",
+      args = get_arguments,
+    },
     {
       type = "go",
       name = "Debug Package",