Improve Test Infrastructure (Part 2)

Follow-Up of #1279

* Improve ```assert_equal``` to take blocks
* dito ```assert_not_equal```
* add ```assert_float``` to check floats with a limited precision
* Improve the following tests: Bootstrap Blocks, Bootstrap Literals, ```Float```, ```GC```, ```IndexError```, ```LocalJumpError```, ```NameError```, ```nil```, ```NoMethodError```, ```Numeric```, ```Object```, ```Proc```, ```RangeError```, ```RuntimeError```, ```StandardError```, ```Symbol```, ```true``` and ```TypeError```