Changes API to case-syntax

This is a major api change which results in a simplification of the API. There are only two major functions now:

1. `Kernel#recovery` which is used in a case statement to define the recoveries attached to a raised Exception.
2. `Kernel#recover` - This used used inside a rescue clause to execute a given recovery.

### C-Extension
The C-extension has been significantly reduced in functionality. It is only needed to provide a hook to ruby code so it can attach the list of captured recoveries. After that, it calls the standard raise method.

### Collector
This is used as a trick to collect recoveries. When passed to a case statement, it works in collaboration with the `Recovery` class by overriding the `===` method. Instead of actually doing a compare it collects the Recovery onto the collector and returns false. When a recovery is invoked, the code returns to inside that method, only this time it returns true.

### Recovery
This is used as the identifier for a `Recovery` instance attached to an `Exception`. It is very similar to the `Exception` class except it is identifying recoveries.

### Exception#recoveries

Shows the list of recoveries attached to an exception. This is useful when `rescue` code is trying ti determine the best recovery to take. Additionally, it can be used in Pry to show the list of recoveries (`Exception#recoveries#inspect`)