rename filters to casters

This frees up the class "Filter" to be used as a model which represents
a filter rather than a data converter.
rename filter spec helper to caster
relabel var from filter to caster to represent the obj being used
replace FilterMethod with Filter

This gets us a basic filter class to work with as we progress. It also
allows us to clean up the code in base by passing a Filter rather than a
bunch of args.
subclass filters by type and throw a NoMethodError when an invalid filter type is called
Merge branch 'master' into overhaul

Conflicts:
	lib/active_interaction/base.rb
no need to be so specific
filters are now broken between those that can have sub filters and those that cannot
no longer throw a NoMethodError

The NoMethodError is thrown on load when you build a filter rather than
when you try to retreive a caster. Now we just let the base error bubble
up.
switch Caster to accept a Filter
add cast method to Caster which finds the correct caster and passes the call on to it
renaming FilterMethods to Filters
do not add FilterWithBlock as a valid filter type
move parsing sub-filters to load time

We're also no longer passing around the block of sub-filters for
processessing. Instead we're creating Filter objects that can be used.
move filter error to load time rather than run time
close #57 by adding an inputs method
add a :focus flag for tests
moving validation into its own module
adding docs for inputs class method on base
Merge branch 'v0.6.0' into overhaul

Conflicts:
	lib/active_interaction/filters/boolean_filter.rb