Not every package follows semantic versioning

[lily-mara]

Currently, Poet assumes that every single package follows semantic versioning, but this is not true. For example, the iterfzf project follows a versioning scheme that indicates both the Python library version, and the version of a bundled executable that the library relies on. Because Poet assumes that every version is a semantic version, it is incapable of installing libraries like iterfzf that use more than 3 dots in their version. The current release of iterfzf is 0.2.0.17.0. Poet parses this as 0.2.0+17.0, and when it tries to download the package with pip, it just tries to download 0.2.0, which does not exist.