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
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