No longer use error code 1 fore "unspecified error".

[nbacquey]

Description

Error code 1 is usually used for

things went well and I need to answer 'no' or 'false' in a clean way

This PR changes the code of "unspecified error" from 1 to 10

Closes #611

Checklist

Checklist before merging:

• [x] CHANGELOG.md updated
• [x] README.md up-to-date