Add adapter for echo framework

[zhangmingke]

Describe what this PR does / why we need it

add adapter for echo framework

• SentinelMiddleware returns new echo.HandlerFunc

• Default resource name is {method}:{path}, such as "GET:/api/:id"

• Default block fallback is returning 429 code

• Define your own behavior by setting options

Does this pull request fix one issue?

Describe how you did it

Describe how to verify it

Special notes for reviews

[sczyh30]

Could you please add some description about your design according to the PR template?

[sczyh30]

And could you please resolve conflicts?

[codecov-io]

Codecov Report

Merging #95 into master will increase coverage by 0.73%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #95      +/-   ##
==========================================
+ Coverage   42.29%   43.03%   +0.73%     
==========================================
  Files          59       61       +2     
  Lines        2480     2512      +32     
==========================================
+ Hits         1049     1081      +32     
  Misses       1311     1311              
  Partials      120      120              

Impacted Files	Coverage Δ
adapter/echo/middleware.go	100.00% <100.00%> (ø)
adapter/echo/option.go	100.00% <100.00%> (ø)

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[sczyh30]

LGTM

[sczyh30]

Nice work. Thanks for contributing!