Fix status conversion in Couchdb Error

[tomsquest]

• Converting the status code from int to string was done using string() instead of strconv.ItoA().
• Test case created.
• Minor fixes/cleanup

[nono]

Thanks for the PR. I was working on the same files, you should look at my PR: #33

[tomsquest]

If there are conflicts between our two branches, could you cherry-pick/apply these/changes and closes this PR (I am not emotionally attached to it 😉 ).

[tomsquest]

@nono Just thinking about it: the status field in ther Error json is a string. Shouldn'it it be kept as an int, or it could be renamed as statusCode (principle of least surprise). WDYT ?

[nono]

@tomsquest we want to stay close to the couchdb API, and couchdb uses status with a string, so we will keep that

[jinroh]

@tomsquest I've merged #33 and opened another PR #35 with your rebased changes.