fix: include parsed .md spec into api.json

[yury-s]

• Add .spec to all classes/members to simplify generation of language-specific docs (such as javadoc).
• Keeping .comment fields too to minimize changes on the python end for now.

Raw api.json size differs by 0.5Mb but zipped one grows by just 31Kb so should not be a problem.

-rw-rw-r-- 1 yurys yurys 681K Mar  1 12:16 api.json
-rw-rw-r-- 1 yurys yurys 1.1M Mar  1 12:15 api.json-both

-rw-rw-r-- 1 yurys yurys 121K Mar  1 12:17 b.zip
-rw-rw-r-- 1 yurys yurys  90K Mar  1 12:17 c.zip