Use :format to define per-currency formatting rules instead of :symbo…

…l_first (RubyMoney#943)

* Add symbol_with_space key to currency config.
Add tests to test the spacing option.

* Make spacing part of currency rules when symbol procede the ammount

* Add :symbol_with_space attribute to currency config.
* Initialize symbol_with_space instance variable for currency object.
* Set '%u %n' format in rules if symbol_with_space value is true for a
  currency.
* Add test cases to cover the change.

* Use :format instead of :symbol_with_space in currency config.

* Add from format instace variable to currrency.
* Use currency format instance variable to format currency only if
  :symbol_position rule is not passed.
* :format rule takes the first priority when passed to rules.

config/currency_backwards_compatible.json

@@ -8,6 +8,7 @@
     "subunit": "Sent",
     "subunit_to_unit": 100,
     "symbol_first": false,
+    "format": "%n %u",
     "html_entity": "",
     "decimal_mark": ".",
     "thousands_separator": ",",
@@ -39,6 +40,7 @@
     "subunit": "Centas",
     "subunit_to_unit": 100,
     "symbol_first": false,
+    "format": "%n %u",
     "html_entity": "",
     "decimal_mark": ".",
     "thousands_separator": ",",
@@ -70,6 +72,7 @@
     "subunit": "Khoums",
     "subunit_to_unit": 5,
     "symbol_first": false,
+    "format": "%n %u",
     "html_entity": "",
     "decimal_mark": ".",
     "thousands_separator": ",",
@@ -100,6 +103,7 @@
     "subunit": "Tennesi",
     "subunit_to_unit": 100,
     "symbol_first": false,
+    "format": "%n %u",
     "html_entity": "",
     "decimal_mark": ".",
     "thousands_separator": ",",