Zepl.vim v1.6

Yet more incremental improvements!

• Added ZeplTerminalWinOpen auto-command that will run when the REPL window first opens. (Thanks @idbrii!)
• Made rlwrap artefacting fix optional with the rlwrap key in b:repl_config to resolve issues with other REPLs.
• Don't startinsert in Neovim terminal when :keep mod was used. (Thanks @jiz4oh!)
• Documentation updates.

Full Changelog: v1.5...v1.6