extract building example part of schemata_example() as build_example()

it might be useful describe some JSON example in render command (e.g. generate JSON request body by link['schema']['properties'] value)
rename build_example to properties_example
Merge pull request #101 from co3k/separate-build-example

extract building example part of schemata_example() as build_example()
[schema] rework properties_example to schema_example, update template to use it