Deprecate the usage of the camelCase attributes

[brunoocasali]

We currently support multiple ways of sending the search attributes:

• index.search('abc', { attributesToCrop: ['description'], cropLength: 5 })
• index.search('abc', { attributes_to_highlight: ['description'] })

and incorrect and weird ways like:

• index.search('abc', { distinct_ATTribute: 'title' })

Since this is not a ruby style of having attributes, we should eliminate it!

TODO:

• Print warning messages when the user called a method with a different typographical convention than snake_case.
• Replace the old way with the new way in the .code-samples.meilisearch.yml

After the two initial steps:

• Drop the support to other styles (removing the code and the warnings).

[brunoocasali]

Fixed by #377 and #470