Support for additional .ghci files in GHCi.
Currently, GHCi only loads a single .ghci file. As a result, all user customizations and macros must be centralized to one location. Additionally, this leaves limited potential for tools using GHCi (cabal-install, for example) to customize the interpretation environment. I propose adding a -ghci-script flag for each additional .ghci file to be loaded in the order specified on the command line after the usual .ghci file in the current or user directory.