Clojure, Java, PHP: remove hardcoded readline history path.
Update README.md and TODO. Minor PS update.
PS: minimal step1_read_print
PS: step2_eval
PS: add step3_env
PS: error handling, throw, print excpetions without dying.
PS: add step4_if_fn_do
PS: fix string length calc for printing integers.
PS: add step5_tco.

Update step4 function definition to match.
README: minor name synchronization ("argument").