Prototype: Separators settings api

[bidoubiwa]

Description
Two new settings named separatorTokens and nonSeparatorTokens are being introduced as a prototype in meilisearch. We would like to create a prototype version of meilisearch-js implementing the required changes to be able to try out the new settings.

Following this specification, we need to add:

• Two GET routes that fetches the settings
• Two PUT routes that updates the settings
• Two Delete routes that resets the settings
• Add the new settings in the Settings types
• Add tests

Basic example

client.index('x').getSeparatorTokens()
client.index('x').getNonSeparatorTokens()
client.index('x').updateSeparatorTokens(["|", "/", "&sep"])
client.index('x').updateNonSeparatorTokens(["@", "#"])
client.index('x').resetSeparatorTokens()
client.index('x').resetNonSeparatorTokens()

[curquiza]

Closed by #1573