snusnu/substation — pull request #6 by snusnu (2013-07-04 03:30:49+00:00)
Title: Build failure chains on top of default failure chains defined in the environment

This branch makes it possible to build on top of default failure chains defined in the environment.

An example:

```ruby
env = Substation::Environment.build do
register :sanitize, Substation::Processor::Evaluator::Data do
wrap Error::SanitizationError
end
end

action = env.chain do
sanitize Some::Sanitizer do
wrap Views::MalformedInput
end
end
```

If the invoking action produces a sanitization error, the sanitizer output will first get wrapped inside `Error::SanitizationError` which in turn gets wrapped inside `Views::MalformedInput`.