Add some test cases and run test cases on binding/render dir

[thinkerou]

Now travis not run some test cases on binding and render dir.
Hi, @javierprovecho @appleboy @tboerger should we add these test case?
Thanks!
The pull request includes the follow points:

• update Makefile for running coverage.sh
• add coverage.sh to run code coverage rate
• add render and binding to coverage.sh
• update binding_test.go which code coverage rate is 99.23%
• update render_test.go which code coverage rate is 100%
• update .gitignore

[codecov]

Codecov Report

Merging #1168 into master will increase coverage by 0.22%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master   #1168      +/-   ##
=========================================
+ Coverage   98.18%   98.4%   +0.22%     
=========================================
  Files          16      34      +18     
  Lines        1432    1757     +325     
=========================================
+ Hits         1406    1729     +323     
- Misses         22      23       +1     
- Partials        4       5       +1

Impacted Files	Coverage Δ
binding/binding.go	100% <0%> (ø)
render/html.go	100% <0%> (ø)
render/text.go	100% <0%> (ø)
binding/xml.go	100% <0%> (ø)
binding/form_mapping.go	98.29% <0%> (ø)
render/render.go	100% <0%> (ø)
binding/query.go	100% <0%> (ø)
render/msgpack.go	100% <0%> (ø)
render/data.go	100% <0%> (ø)
binding/msgpack.go	100% <0%> (ø)
... and 8 more

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[thinkerou]

squash commits and reopen the pull request.

[appleboy]

@thinkerou Thanks.