so that Producer::send can just take the Message cpp-side

also fix service_url handling in bin/example-*

also, switch the using Module#prepend to decorate C++ defined methods
with ruby, rather than `_` prefixes

leave the placeholder in the C++ binding code, but don't actually bind
it, and don't use it in the example

to see if it makes a difference for where bundler puts the bindings.so
file. right now it's putting it in `lib/` instead of in `lib/pulsar/`

and use them in the example producer and consumer

and fix the topic name back to what it had been

still allow passing in the enum value integer directly, but also for
convenience translate a set of symbols too and from the enum values

This should fix this error that I ran into when using listen_in_thread:
```
bundler: failed to load command: ./client.rb (./client.rb)
LocalJumpError: no block given (yield)
  /home/docker/.gem/ruby/2.6.0/bundler/gems/pulsar-client-ruby-f915f9680abd/lib/pulsar/consumer.rb:42:in `listen'
  /home/docker/.gem/ruby/2.6.0/bundler/gems/pulsar-client-ruby-f915f9680abd/lib/pulsar/consumer.rb:48:in `block in listen_in_thread'
```

including allowing forwarding Hash argument from Client#subscribe

accidentally built and published .3 without the fix

inverted logic error checking sufficient environment, and a bare `gets`
tries to read from ARGV[0], when present, instead of the intended STDIN

…ion loader

…ronment

…Result.h

Adding close call to producer and consumer

- added Gemfile.lock
- default rake command also compiles project
- installed libpulsar in Travis container

Add CI support to project

Use pulsar 2.6.1 in CI

Add silent_logging option to silence the c++ logger

Update gem version to match pulsar lib version

chore(docs): fixed minor version problem in README

Do live pulsar produce/consume in tests when configured

Allow consumer to subscribe to multiple topics

Add topic getter to message class

add enum values for setting subscription position type