Add AppVeyor config to move away from Travis

[sanathkr]

Issue #, if available:

Description of changes:

Description of how you validated changes:

Checklist:

• Write/update tests
• make pr passes
• Update documentation
• Verify transformed template deploys and application functions as expected
• Add/update example to examples/2016-10-31

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-io]

Codecov Report

Merging #1263 into develop will decrease coverage by 0.02%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop    #1263      +/-   ##
===========================================
- Coverage    94.48%   94.46%   -0.03%     
===========================================
  Files           72       78       +6     
  Lines         3738     4334     +596     
  Branches       740      854     +114     
===========================================
+ Hits          3532     4094     +562     
- Misses         104      114      +10     
- Partials       102      126      +24

Impacted Files	Coverage Δ
samtranslator/model/eventsources/pull.py	82.05% <0%> (-12.07%)	⬇️
samtranslator/model/sam_resources.py	95.1% <0%> (-0.53%)	⬇️
samtranslator/plugins/api/implicit_api_plugin.py	98.23% <0%> (-0.39%)	⬇️
samtranslator/model/naming.py	100% <0%> (ø)	⬆️
...amtranslator/policy_template_processor/template.py	100% <0%> (ø)	⬆️
...mtranslator/policy_template_processor/processor.py	100% <0%> (ø)	⬆️
...nslator/model/preferences/deployment_preference.py	100% <0%> (ø)	⬆️
samtranslator/sdk/resource.py	100% <0%> (ø)	⬆️
samtranslator/model/exceptions.py	100% <0%> (ø)	⬆️
samtranslator/translator/verify_logical_id.py	100% <0%> (ø)	⬆️
... and 20 more

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