Header/metadata fix

[erikyo]

this PR fix the issue around the missing data, but still some enhancements could be done

• some package json data like "bug" can be both string or object but currently only the string version is captured
• the email author is optional for the pot file header but is missing in the WordPress plugin or header
• also composer.json can provide some info but currently isn't parsed at all

close #9

[johnhooks]

@erikyo I'm getting some odd output, its labeling as comming from the style.css but I don't have one in my project.

#: style.css
#. Name of the vinyl
msgid "@wp-blocks/vinyl"
msgstr ""

#: style.css
#. Author of the vinyl
msgid "undefined"
msgstr ""

#: style.css
#. Description of the vinyl
msgid "An audio player WordPress block."
msgstr ""