Fix "successful" typos

A number of s/succesful/successful/ across the tree. There is also a
"successfull" typo in a comment in snappy.c but in the interest of not
creating spurious diffs with a third-party upstream, this was left alone
deliberately.
Fixed uninitialized variable warning
Removed outdated C++ example
Added consumer documentation to INTRODUCTION.md
Proper fallthrough for -X "topic." properties
Periodic metadata requests could occassionally be flooded.
Add support for auto-creating topics on broker (issue #22)

This requires "auto.create.topics.enable=true" to be configured on the
brokers.

The automatic topic creation trigger (a topic-specific metadata request)
is performed every second, as well as immediately when a new topic is added
if at least one broker is up.
Clarified comment