Fix str doc return contract.
update current-readtable in #%module-begin so that #fn works in repl
update current-read-interation in configure-runtime submodule
use #:language-info instead of modifying #%module-begin
Add Racket 6.1 and 6.1.1 to matrix.
Merge pull request #46 from AlexKnauth/repl-fn-lit

let #fn work in the repl using #:language-info and runtime-config.rkt
Simplify `configure`.

As discussed here:

  https://github.com/greghendershott/rackjure/pull/46#issuecomment-64031796