Add feature flags for Lucide categories

[DanielleHuisman]

Before trying to publish this package, there were features for every icon. Unfortunately, crates.io has a limit of 300 features, so publishing was not possible. See this article for more information about the feature limit.

Adding features flags for categories would be feasible, because there are only 43 Lucide categories at the moment. This could significantly decrease compile times when enabling only the required categories for a project.

Related issues: #20.