Searchable booleans in front matter

[ysim]

e.g.

• tested: no
• can_freeze: yes
• batch_optimized: yes

Should accept the values:

• yes, true, 1
• no, false, 0

Acceptance criteria:

• Able to search on boolean fields

• Presence of boolean fields in front matter will not result in this warning being logged:

  {"file":"/path/to/recipefile.md","level":"warning","msg":"Unknown type detected in front matter","time":"2020-07-24T15:37:57-04:00"}