S3 Delete Updates

[michaelconnor00]

• Refactored s3 delete to use boto3 resource which has built in pagination, so there is no 1000 item limit. #783
• Added delimiter option for more granularity when filtering keys. #784
• A list_contents command was added, mostly for aid in testing.

[codecov-io]

Codecov Report

Merging #800 into dev will increase coverage by 0.4%. The diff coverage is 98.66%.

@@            Coverage Diff            @@
##              dev     #800     +/-   ##
=========================================
+ Coverage   80.47%   80.88%   +0.4%     
=========================================
  Files          86       87      +1     
  Lines        6029     6088     +59     
=========================================
+ Hits         4852     4924     +72     
+ Misses       1177     1164     -13

Impacted Files	Coverage Δ
tests/unit/test_s3.py	100% <100%> (ø)	:arrow_up:
tests/unit/moto_test_data.py	100% <100%> (ø)
gbdxtools/s3.py	57.77% <96.29%> (+24.01%)	:arrow_up:

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[michaelconnor00]

Fixed Travis and Appveyor builds. Also changed the merge target to dev. Ready to merge.