New option to plsql-spec command to indicate when to capture the output

The idea with this commit, is to provide a way to show the output when Thor runs the rspec command, 

In this commit @rsim added the option to Capture the log, and there is no way to disable the option :(
https://github.com/rsim/ruby-plsql-spec/commit/8c76f47fdfec17c1a1a41162b894a5df116b0a5c

The problem with :capture => true is that hide errors that are outside rspec, I ask about this option in the Google Group: 
https://groups.google.com/forum/?fromgroups=#!topic/oracle-enhanced/SmkETvkc2i8

I added a new option "--capture" to "plsql-spec" in order to indicate when do you **don't** want to capture the errors:
```ruby
    plsql-spec run  --capture=false
```

If you don't provide the capture option, the default value is true (How it works today)
```ruby
    plsql-spec run
```

In this example I have an error in the test_spec.rb file, I'm requiring a non existing gem
```ruby
require "spec_helper.rb"
require "non_existing_gem"
``` 
Before my commit, this is the output
rake probar[ejemplo] executes internally the "plsql-spec" run command

It's very difficult to catch the error
![notes marker](http://i.imgur.com/mFlyHbv.png)


After the commit, with plsql-spec run --capture=false this is the output
![notes marker](http://i.imgur.com/TrkFHyv.png)