[BUGFIX] Require only Bundler groups appropriate to application environment

Fixes #403
[UPDATE] Drop support for Ruby 1.9.2
[DOC] Clean up changelog
[FEATURE] Allow preventing automatic call hangup after controller completion

Set `Call#auto_hangup = false` prior to controller termination.

Fixes #407
Merge pull request #425 from adhearsion/feature/open-ended-outbound-calls

[FEATURE] Allow preventing automatic call hangup after controller completion
[FEATURE] Allow specifying a pre-join callback to #dial

This is executed once prior to joining a call, and is passed the outbound call being joined.

#423
[FEATURE] Allow specifying rinback to `#dial` as a collection of audio
[FEATURE] Allow specifying ringback as a callback to start
[DOC] Fix changelog
[UPDATE] Depend on more recent Punchblock

Only just got output repeat support on Asterisk
Merge branch 'feature/dial_custom_ringback' into develop
[FEATURE] Generated apps now encourage storing most app code in `app/`, which is in the load path

Nothing in this directory is auto-loaded, but can be easily required without messy relative paths.

#352
[BUGFIX] Call event handlers now cannot crash the call, and no longer stop on return value

Fixes #426
Merge pull request #429 from adhearsion/feature/cleaner_app_layout

[FEATURE] Generated apps now encourage storing most app code in `app/`, which is in the load path
[DOC] Registering call event handlers

Fixes #417
[DOC] Call#execute_controller API docs
[FEATURE] Generate applications with an explicit dependency on Punchblock

* Many users of Adhearsion make direct use of Punchblock APIs (mostly command models) which are subject to Punchblock's own versioning.

* Adhearsion occasionally bumps the dependent Punchblock major version number in minor releases to gain access to new functionality that required such a bump in Punchblock, on the basis that this does not impact Adhearsion's API itself.

These two facts combine to produce the potential for breakage of an Adhearsion application by updating the Adhearsion minor version.

Generating an application with a specific dependency on Punchblock prevents bumping the Asterisk version if it requires a major version of Punchblock greater than the app was generated in, forcing the user to manually update the Punchblock version in their Gemfile at this point. This forces the user to consider their Punchblock API dependency and prepare for potential breakage.
[DOC] Better warning in Gemfile
Merge pull request #430 from adhearsion/feature/explicit_punchblock_dependency

[FEATURE] Generate applications with an explicit dependency on Punchblock
[BUGFIX] Ensure PB version is accessible in generator