Make `name` and `version` arguments mandatory

[alcarney]

Description (e.g. "Related to ...", etc.)

I think in #274 we said we wanted to make the name and version arguments to a LanguageServer object mandatory? This PR removes the warning and default arguments meaning they now have to be provided by the language server author.

Code review checklist (for code reviewer to complete)

• [x] Pull request represents a single change (i.e. not fixing disparate/unrelated things in a single PR)
• [x] Title summarizes what is changing
• [x] Commit messages are meaningful (see this for details)
• [x] Tests have been included and/or updated, as appropriate
• [x] Docstrings have been included and/or updated, as appropriate
• [x] Standalone docs have been updated accordingly
• [x] CONTRIBUTORS.md was updated, as appropriate
• [x] Changelog has been updated, as needed (see CHANGELOG.md)

[tombh]

(Saw you fix the test as I was typing 😏)

Well remembered! The v1 release is the perfect moment to include this.