+1 failing test: function spec
+1 test pass: function spec (empty function)
+2 test pass: function returning null
refactored test contexts to use shared examples
+1 failing test: function returning 0
+1 test pass: function returning literal number(0)
+3 passing tests: function returning literal object
+4 faililng test: function expression receiving and returning one argument
refactor: moved expresion parsing to process_expresion, and let statement parsing on process, +1 test pass: functions with one argument are now callable
+3 passing tests: function expression receiving and returning one argument
refactor: renamed method Processor#process_expresion to Processor#process_expression
+3 passing test: reading variable of parent scope
+2 passing test: function assigning variable out of scope
+3 failing test: function defining variables
+3 passing test: functions defining variables
+2 passing tests: variable declared with complex expression
refactor: splitted JSObject and JSScope