Update readme, make it more clear to use httptest

 at first glance that we should use httptest
fix spelling
Allow Contains and NotContains to check slices and arrays
Increase assert test coverage from 86.6% to 97.1%, fixed bugs.

Extend tests for NotEqual, Len and add tests for Condition, InEpsilon.
Add tests for Assertion.Condition, Assertion.InEpsilon, Assertion.InDelta
Fix a bug for Assertion.InDelta, Assertion.InEpsilon having incorrect signature.
Minor doc string update
Include sentence about using mockery
Fix grammer on assert.Len()

:hamster:
Merge pull request #80 from capoferro/patch-1

Fix grammer on assert.Len()
Merge pull request #76 from victorkryukov/master

Increase testify/assert test coverage from 86.6% to 97.1%, fix bugs.
Merge pull request #78 from evanphx/patch-1

Include sentence about using mockery
Merge pull request #73 from comogo/includes

Allow Contains and NotContains to check slices and arrays
Update readme, make it more clear to use httptest

Fix #64
Merge pull request #85 from stretchr/joshrendek-patch-1

Joshrendek patch 1
Implement Regexp and NotRegexp
Implement HTTP(Success|Error|Redirect) and HTTPBody(Not)Contains
Merge pull request #86 from victorkryukov/regexp

Implement Regexp and NotRegexp
Merge pull request #87 from victorkryukov/http-patch

Implement HTTP(Success|Error|Redirect) and HTTPBody(Not)Contains
Merge branch 'master' of https://github.com/stretchr/testify into sed_script
Two significant changes:
* Every test now begins with assert := assert.New(suite.T()), so that you don't have to repeat "suite.T() with every assertion.
* Added special conversions for IsNil err, and Not(IsNil) err -> NoError(err) and Error(err) respectively.