Change CI/CD

[MKoesters]

Enhance our CI/CD Pipeline

• Use tox for testing pymzML in different in environments for python 3.5 to 3.7
• Test example scripts
• Check code coverage and use codecov for commenting statistics on pull requests
• Automatically deploy tags to pypi using travis

[codecov[bot]]

Codecov Report

Merging #140 into master will increase coverage by 65.98%. The diff coverage is 80.6%.

@@             Coverage Diff             @@
##           master     #140       +/-   ##
===========================================
+ Coverage   15.94%   81.92%   +65.98%     
===========================================
  Files          13       32       +19     
  Lines        1844     3381     +1537     
===========================================
+ Hits          294     2770     +2476     
+ Misses       1550      611      -939

Impacted Files	Coverage Δ
tests/file_io_indexed_gzip_reader_test.py	96.55% <ø> (ø)
pymzml/file_interface.py	93.33% <100%> (+53.33%)	:arrow_up:
pymzml/file_classes/indexedGzip.py	96.96% <100%> (+54.54%)	:arrow_up:
tests/utils_decoder_test.py	66.66% <100%> (ø)
tests/file_io_standard_mzml_test.py	96.29% <100%> (ø)
tests/main_ms_numpress_test.py	97.94% <100%> (ø)
pymzml/regex_patterns.py	100% <100%> (ø)	:arrow_up:
pymzml/file_classes/standardGzip.py	97.14% <100%> (+60%)	:arrow_up:
tests/main_chromatogram_test.py	89.47% <100%> (ø)
tests/test_file_paths.py	100% <100%> (ø)
... and 49 more

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