Subcollections should be documented

[jackfirth]

Currently the relevant subcollections are:

• lens/base
• lens/list
• lens/hash
• lens/syntax
• lens/struct
• lens/applicable (re-exports lens)

Note that once documented, changing the names or paths of subcollections is a breaking change. Therefore, prefer not to expose subcollections unless they are of significant size.

[jackfirth]

For 1.0, it's only necessary that the two modules lens and lens/applicable be documented. All other subcollections should be undocumented so as not to commit to something that may later change. lens/base may be an exception to this, though it's not strictly necessary for 1.0

[jackfirth]

Moving into backlog as it no longer blocks 1.0

[jackfirth]

Closing in favor of issues for specific subcollections, e.g. #108