Include exception cause in error output

[thekid]

Before:

$ xp lambda test Env | tail -1 | json_pp
{
   "errorMessage" : "Test",
   "errorType" : "lang.IllegalArgumentException",
   "stackTrace" : [
      "Env::{closure}(...) (line 132 of AwsRunner.class.php)",
      "xp.lambda.AwsRunner::main(...) (line 389 of class-main.php)",
      "Env::{closure}(...) (line 132 of AwsRunner.class.php)",
      "xp.lambda.AwsRunner::main(...) (line 389 of class-main.php)"
   ]
}

After:

$ xp lambda test Env | tail -1 | json_pp
{
   "errorMessage" : "Test",
   "errorType" : "lang.IllegalArgumentException",
   "stackTrace" : [
      "Exception lang.IllegalArgumentException (Test)",
      "Env::{closure}(...) (line 112 of AwsRunner.class.php)",
      "xp.lambda.AwsRunner::main(...) (line 389 of class-main.php)",
      "Exception lang.IllegalStateException (Cause)",
      "Env::{closure}(...) (line 112 of AwsRunner.class.php)",
      "xp.lambda.AwsRunner::main(...) (line 389 of class-main.php)"
   ]
}

[thekid]

Here's a real life scenario where this is helpful:

Without the cause message, we would only be seeing the stack trace, and it wouldn't be as obvious why the request has failed. In this case, this is because the "zlib" extension isn't loaded (see #8)

[thekid]

Released in https://github.com/xp-forge/lambda/releases/tag/v4.2.0