Rule: no nested try…catch blocks

##### rule
>  Do not nest `try…catch` blocks

```erlang
bad() ->
  try
    maybe:throw(exception1),
    try
      maybe:throw(exception2),
      "We are safe!"
    catch
      _:exception2 ->
        "Oh, no! Exception #2"
    end
  catch
    _:exception1 ->
      "Bummer! Exception #1"
  end.

good1() ->
  try
    maybe:throw(exception1),
    maybe:throw(exception2),
    "We are safe!"
  catch
    _:exception1 ->
      "Bummer! Exception #1";
    _:exception2 ->
      "Oh, no! Exception #2"
  end.

good2() ->
  try
    maybe:throw(exception1),
    a_function:that_deals(with, exception2),
    "We are safe!"
  catch
    _:exception1 ->
      "Bummer! Exception #1"
  end.
```

##### reasoning
Nesting `try…catch` blocks defeats the whole purpose of them, which is to isolate the code that deals with error scenarios from the nice and shinny code that deals with the expected execution path.