Improve error logging

[RichardAtkin]

Background
The Python awslambdaric v2.0.0 library works perfectly in conjunction with awslambdarie in local dev, and it usually works great in 'proper' Lambda, but unfortunately not all the time. When I invoke some particular in-house libraries while running in Lambda, the invocation dies without giving an insightful reason.

Problem
The provided error 'Runtime exited with error: exit status 1' does not help me debug why a fault is happening.

Suggested fixes

• Document what could cause awslambdaric / Lambda to die and return a runtime exiterror 1
• Provide detailed outputs in the execution log about what has just caused the fault