Renaming the package to r-tree

[BurningWitness]

• Renamed RTree.D2 into R2Tree for future-proofing;
• Cleaned up small bits of documentation;
• Renamed package to r-tree and reset the version to 1.0.0.0.

@sebastian-philipp I wish to publish this on Hackage as r-tree and I wish to deprecate data-r-tree (for the latter I need maintainer rights for the package, either granted by you directly or via an email to trustees). My maintainer account is this one.

[sebastian-philipp]

Done, See https://hackage.haskell.org/package/data-r-tree

[sebastian-philipp]

Thank you for really looking into this! This is really awesome! https://hackage.haskell.org/package/r-tree

[BurningWitness]

Note also that I took over the radix-tree package, so if you feel like deprecating data-stringmap you can choose that as a package to point to. (although I could say the same about bytestring-trie, which has been out for more than a decade)