generate Markdown document from texinfo

[takahashim]

It's a bit difficult to read protocol spec. in Texinfo on editors, so add a new task to convert into markdown and generated md file.

[valich]

Thank you! LGTM, however I think it's really better and somewhat easier to move doc/protocol-spec.texi to markdown completely. What do you think?

Also, unfortunately, has not been maintained since gem adoption so we need to document all the features from the last years..

BTW @takahashim what's your use case for ruby-debug-ide?

[hurricup]

Closing this as abandoned