feat: fromyaml and toyaml

[dormeiri]

toyaml example:

echo '{"fruits":["apple","banana"]}' | gojq '.fruits | toyaml'
# Output: "- apple\n- banana"

fromyaml example:

echo '{"fruits":"- apple\\n- banana"}' | gojq '.fruits | fromyaml'
# Output: ["apple","banana"]

Fixes #277