add a new endpoint for testing a 200 with no body

add a new endpoint returning an OK status but with content-length 0
Add a failing test case
handling a zero content-length

a server can return a 200 state without returning any body, it's a
valid response if the content-length is 0
bump version
Merge pull request #14 from kentaromiura/fix-content-length-0

Fix content length 0