BentoML configuration base

[parano]

• implementation of python configparser and env var based configuration
• added apiserver config as an example

Breaking change:

• changed home folder from ~/.bentoml to ~/bentoml

[codecov-io]

Codecov Report

Merging #158 into master will increase coverage by 0.4%.
The diff coverage is 71.29%.

@@            Coverage Diff            @@
##           master     #158     +/-   ##
=========================================
+ Coverage   60.98%   61.39%   +0.4%     
=========================================
  Files          48       49      +1     
  Lines        1879     1971     +92     
=========================================
+ Hits         1146     1210     +64     
- Misses        733      761     +28

Impacted Files	Coverage Δ
bentoml/server/gunicorn_server.py	63.15% <100%> (ø)	⬆️
bentoml/deployment/sagemaker/__init__.py	20.51% <100%> (ø)	⬆️
bentoml/archive/loader.py	83.33% <100%> (ø)	⬆️
bentoml/__init__.py	100% <100%> (ø)	⬆️
bentoml/cli/__init__.py	43.92% <100%> (ø)	⬆️
bentoml/exceptions.py	100% <100%> (ø)
bentoml/archive/py_module_utils.py	91.13% <100%> (ø)	⬆️
bentoml/deployment/serverless/__init__.py	22.4% <100%> (ø)	⬆️
bentoml/service.py	87.73% <100%> (ø)	⬆️
bentoml/handlers/image_handler.py	57.81% <100%> (ø)	⬆️
... and 6 more

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