This way developers will see any potential missing context without
running the entire filter, which may not ever encounter a case where
it needs the context.

Declaring required contexts has been simplified.
validates_context_presence no longer requires self to be passed in.
Instead it will attempt to build the caller name by using
Kernel::caller.

Tests have been added for filters that require context.

Noted in filters if a context is required. Updated README to include info about
required contexts.

Using a singleton to remove the reliance on a class variable.

Removed unnecessary calling_class method and just using self instead.

This way developers will see any potential missing context without
running the entire filter, which may not ever encounter a case where
it needs the context.

Declaring required contexts has been simplified.
validates_context_presence no longer requires self to be passed in.
Instead it will attempt to build the caller name by using
Kernel::caller.

Tests have been added for filters that require context.

Noted in filters if a context is required. Updated README to include info about
required contexts.

Using a singleton to remove the reliance on a class variable.

Removed unnecessary calling_class method and just using self instead.

…-pipeline into context_validation

Removed declarative code in favor of a validation hook. It's up to subclasses
to implement the validate method. Validate will be called by Filter after
initialization so @context is available.

Reverted README.md to remove the additions about validation.

Changed required context method name to 'needs.' Updated needs to use
@jbarnette's concise version of needs.

Made validate a noop method instead of checking if a filter respond_to?
validate.