Add an option to minify the output.

This line is formatting the json schema output. I have some files generated by this tool with 5K+ lines, and just by not formatting the output, i can reduce around 2K lines.

https://github.com/vega/ts-json-schema-generator/blob/1f22dda8ec2ec9470788da0f5b2129ca692bf611/ts-json-schema-generator.ts#L64

An option `--no-format` can resolve this issue.