writeYAMLmodel: YAML 1.1 booleans such as NO are written unquoted #10

needsQuote in src/io/writeYAMLmodel.m quotes the YAML 1.2 booleans (true, True, TRUE, false, False, FALSE) but not the YAML 1.1 ones. A metabolite named NO (nitric oxide) is therefore written as

- name: NO
- formula: NO

and a YAML 1.1 loader such as PyYAML reads both values as False:

>>> yaml.safe_load("- name: NO")
[{'name': False}]

Human-GEM's model/Human-GEM.yml has this for MAM02609c and MAM02609e. It also has formula: Y (MAM02022) and 212 compartment: n values. PyYAML reads y and n as strings, but they are booleans in the YAML 1.1 spec.

Proposal: also quote y, n, yes, no, on and off in any case. raven-toolbox ports this function and has the same gap; it is fixed there in CompMetEng/raven-toolbox#179 (issue CompMetEng/raven-toolbox#178), so that both writers keep writing the same bytes.