Feature/es extra tests

[antoniomaciej]

• Fix parsing Spanish zero.
• Delete unnecessary condition for avoiding plural of Spanish word for a third.
• Add missing test cases for full coverage of format_es.py and the es_number_parse method.
• Add ES suffix to ARTICLES collection in common_data_es, according to the convention used across this library. (This line of code is not executed by any unit test, but it also does not seem to be any references to it in the library.)

[devs-mycroft]

Hello, @antoniomaciej, thank you for helping with the Mycroft project! We welcome everyone
into the community and greatly appreciate your help as we work to build an AI
for Everyone.

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You retain ownership of the code, this is just a license.

Please visit https://mycroft.ai/cla to initiate this one-time signing. Thank
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[krisgesling]

Hi Antonio,

Just checking in to see if you're interested in having this code merged still? I haven't looked at the detail since there's no CLA. But if you're happy to sign a CLA we can get it updated, reviewed and merged.

If not, that's totally fine too.

Thanks