I/O control for non-streaming jars issue #644

I followed @davidmarin suggestion. It doesn't have documentation or
tests yet but it seems to work in my limited trials. Let me know what
you think.

Signed-off-by: Tim Henderson <tim.tadh@gmail.com>
Input markers are now not auto added
Documentation for changes to JarStep.

This documents how Jar step now works. I provide some code docs on
how the input/output is added to the step_args and some usage docs.

Signed-off-by: Tim Henderson <tim.tadh@gmail.com>
Merge branch 'master' into bug/non.streaming.jar
Merge branch 'master' of github.com:Yelp/mrjob into hadoop_jar_io
Merge branch 'bug/non.streaming.jar' of github.com:timtadh/mrjob into hadoop_jar_io

Conflicts:
	mrjob/emr.py
simplified JarStep argument interpolation
renamed _s3_step_* functions to simply _step_*, which is more correct
add jar step io interpolation to hadoop runner
stop pretending Python is Coffeescript
don't interpolate nonexistent step_args
account for step_args being None
add timtadh to __credits__
catting a file *containing* an error is not an error
Merge pull request #807 from bukzor/buck-fix-cat-errlog

catting a file *containing* an error is not an error
Merge branch 'master' of github.com:Yelp/mrjob into hadoop_jar_io
removed unnecessary and confusing annotation from comment
added working example of combining JarSteps and python steps
renamed v0.4 to v0.4.0, for consistency
fixed docs for mrjob.step