Use Ruby string formatting for handling variable replacement

[stevendaniels]

Use Ruby string formatting for handling variable replacement

Currently, @ is used for handling variables and variable replacement in
WebMinion. As an alternative, I suggest we use Ruby's built in string formatting for handling variables in WebMinion configurations.

Currently, the JSON for variable replacement looks like this:

{
  "config": {},
  "flow": {
    "name": "Variable Replacement",
    "actions": [
      {
        "name": "Fill Form",
        "key": 1,
        "steps": [
          {
            "name": "Fill in username",
            "method": "fill_in_input",
            "retain_element": true,
            "target": {"id": "inputEmailHandle"},
            "value": "@username"
          }
        ]
      }
    ]
  }
}

With String formatting, it would look like this:

{
  "config": {},
  "flow": {
    "name": "Variable Replacement",
    "actions": [
      {
        "name": "Fill Form",
        "key": 1,
        "steps": [
          {
            "name": "Fill in username",
            "method": "fill_in_input",
            "retain_element": true,
            "target": {"id": "inputEmailHandle"},
            "value": "%{username}"
          }
        ]
      }
    ]
  }
}

Since the variables are passed in as a hash, replacement would be very simple:

json_configuration % vars # => all variables that can be replaced, do get replaced