Proposal: modify `Read` instances for `Float` and `Double`

Hello, I am working on a small GHC extension to support floating point literals in hexadecimal notation (https://github.com/ghc-proposals/ghc-proposals/pull/37), which is similar to what's available in other languages. To support this change, I would like to propose that we modify the `Read` instances for `Float` and `Double` to parse literals in the new notation. This may affect existing programs---although it doesn't seem very likely. Here is an example: current behavior: reads "0x10p10" = [(16.0,"p10")] new behavior: reads "0x10p10" = [(16384,"")] What do people think? -Iavor