One reader/writer handle many file types, i.e. csv reader for csv and tsv

[chfw]

With your PR, here is a check list:

• Has Test cases written
• Has all code lines tested
• Has make format been run?
• Please update CHANGELOG.yml(not CHANGELOG.rst)
• Passes all Travis CI builds
• Has fair amount of documentation if your change is complex
• run 'make format' so as to confirm the pyexcel organisation's coding style
• Please add yourself to 'contributors' section of pyexcel-io.yml (if not found, please use CONTRIBUTORS.rst)
• Agree on NEW BSD License for your contribution

[codecov-commenter]

Codecov Report

Merging #81 into dev will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##              dev      #81   +/-   ##
=======================================
  Coverage   96.88%   96.89%           
=======================================
  Files          51       46    -5     
  Lines        3212     3189   -23     
=======================================
- Hits         3112     3090   -22     
+ Misses        100       99    -1     

Impacted Files	Coverage Δ
pyexcel_io/readers/__init__.py	100.00% <ø> (ø)
pyexcel_io/writers/__init__.py	100.00% <ø> (ø)
pyexcel_io/database/exporters/django.py	100.00% <100.00%> (ø)
pyexcel_io/database/exporters/sqlalchemy.py	100.00% <100.00%> (ø)
pyexcel_io/database/importers/django.py	97.95% <100.00%> (ø)
pyexcel_io/database/importers/sqlalchemy.py	95.00% <100.00%> (ø)
pyexcel_io/reader.py	97.40% <100.00%> (ø)
pyexcel_io/readers/csv_content.py	100.00% <100.00%> (ø)
pyexcel_io/readers/csv_in_file.py	100.00% <100.00%> (ø)
pyexcel_io/readers/csv_in_memory.py	100.00% <100.00%> (ø)
... and 7 more

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