Fix #37

[sorawee]

Parse 'collection and 'implies when we retrieve the information. This is done in a way that is as compliant with the existing format as much as possible for valid values. However, invalid values will be explicitly marked / quoted so that they cause no trouble.

Two significant changes for valid values:

• a 'core in 'implies will be further wrapped in a list to distinguish a symbol from a string.
• a 'use-pkg-name will be further wrapped in a list to distinguish a symbol from a string.

These two break the compliance, but originally it's not possible to unambiguously use this information anyway.

[sorawee]

Please don't merge this yet. I meant this to be a PR for discussion.