Make http types directives analysable

[chrisnovakovic]

Proposed changes

The syntax of http types blocks is distinct, in that their child directives are arbitrary MIME types - they therefore can't be analysed when strict or check_ctx are enabled, and no meaningful analysis can be performed when check_args is enabled because the arity of child directives is unknown. Skip the checks performed when strict and check_ctx are enabled, and hint to the analyser that all directives inside a types block accept one or more arguments so that a meaningful check can be performed when check_args is enabled.

Fixes #101.

Checklist

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto master
• I will ensure my PR is targeting the master branch and pulling from my branch from my own fork

[chrisnovakovic]

I've just realised that map works broadly similarly to types, so map also isn't analysed correctly at the moment (see #103). It's possible to fix the analyser so both issues are solved at the same time, but the fix is substantially different to the one here (which TBH is a bit of a kludge anyway) so I'll close this PR and open a new one.