Reimplement Form objects as Typed

[ncallaway]

Rename form objects to Typed (exact name is open for discussion).

Create coherent plan around:

• Type checking
• Validation
• Serialization

Change dependencies to implement the above.

[wkirby]

Typed is fine with me. Possible alternatives might include:

• Bundle
• DTO (#java) (also #technicallywrong since we include other functionality besides data accessors)
• Object
• Model (might be too loaded a term in the Ruby world)
• Serializable
• Packet
• Message
• ValueObject or Values

[ncallaway]

Struct is also a popular one.

[Crisfole]

Not necessary for 0.4.0 (which we should dub 1.0.0 btw.