include LICENSE text to subcrates

[igor-raits]

This would help me in packaging for Fedora.

[cramertj]

Ping @lifthrasiir @SimonSapin -- can you add these LICENSE files? Also, is there a reason that the subcrates are CC0 rather than MIT like the main crate?

[cramertj]

Ping @lifthrasiir @SimonSapin

[Chaostheorie]

For anyone attempting to solve the same problem, I can recommend cargo-about, which solves the problem of including the texts. Though this issue seems rather stale anyways.