Set the handles used for --client to use UTF-8

Previously they were binary-mode, so they used `char8` “encoding”, taking
codepoint values modulo 256, leading to cryptic identifier mangling errors
when using idris-vim.
I was going through and replacing readFiles, writeFiles, hGetLines, and hPutStrLn with versions from [System.IO.UTF8](http://hackage.haskell.org/package/utf8-string-0.3.8/docs/System-IO-UTF8.html)
for #94.
Would you think these lines should also get similiar treatment, or the hSetEncoding calls, or both?
Speaking of things to cat set on a handle - I was wondering if LineBuffering mode should be set, or what the default is?