v2.3.0

Added

• Add {BumpVec, BumpString}::shrink_to

Changed

• Improve performance of retain (using std's new implementation)
• Improve performance of alloc_iter*, alloc_fmt* and shrink_to_fit (by making shrink_to_fit exit early when capacity and length are the same)
• Improve documentation

Fixed

• Fix compilation with feature "nightly-clone-to-uninit" and without "panic-on-alloc"