various small improvements

[tage64]

This PR introduces a collection of small improvements to the crate, which was originally developed out of practical need.
The most significant breaking change is that the FixedSliceVec struct has been moved out of the vec module and promoted to a top-level item. This felt more intuitive, as FixedSliceVec is by far the most important data structure in the crate and the primary reason it exists.
In addition, several new methods have been added to FixedSliceVec. Please see the individual commits for more detailed information about these changes.

Commits

• Remove the single module and rename vec.rs to lib.rs. (Breaking Change)
• fix clippy warning
• Update authors list
• Add into_storage() and into_byte_storage() methods
• Implement remove_range()
• fix fmt
• implement into_slice()
• mark the crate no_std
• add extend_from_slice()