Embed metadata in comments

#67

tfcmt embeds metadata into comment with github-comment-metadata. tfcmt itself doesn't support hiding old comments, but you can hide comments with github-comment's hide command.

embedded_var_names

#108 #115

If you want to embed variables passed by -var option, you have to specify variable names by embedded_var_names in the configuration.

embedded_var_names:
- name