Add license detection

[Jake-Shadle]

This is a fairly large change that essentially pulls in a bulk of the https://github.com/jpeddicord/askalono crate to add the ability to detect the SPDX license for a file. For now this is basically just a copy of the code with minor tweaks, but opens up the possibility to make changes more easily in the future, eg. detecting multiple licenses in the same file.

The only major change made when inlining the askalono code into this crate was how the cache is serialized and used. askalono used msgpack (via rmp-serde) for de/serialization, which ended up being the impetus for finally doing this PR and addressing the fairly old issue of #67.

• Remove paste dependency 3Hren/msgpack-rust#372 this PR to remove paste (which has an unmaintained advisory) has others interested in getting rid of it, but since rmp-serde is effectively unmaintained has been sitting, though not as long as another PR that attempts to address the same issue
• Replace rmp-serde with msgpacker jpeddicord/askalono#102 was made to change from rmp-serde to msgpacker as a backwards-compatible change, but as stated previously, askalono is also effectively unmaintained

In light of this, the biggest single change I did while inlining the askalono code was to use a really simple length-prefixed style format for serializing the cache data that doesn't use any external dependencies since the data is incredibly simple and doesn't need to interface with anything outside of itself.

Resolves: #67