stop painting standard error red
add new interactive interpreter subclass with pretty pygments traceback coloring
Incorporate new interpreter class into the main repl and use our write traceback method to send to standard error.
stop str-ing in Interp.write, send FmtStr to stderr instead
factor out redundant code from showtraceback and showsyntaxerror
add test for interpreter
Merge pull request #368 from mlauter/master

Fix #194