aasm/AASM4.md

Planned changes for AASM 4

• done: firing an event does not require to_state parameter anymore (closing issues #11, #58, #80)
• don't allow direct assignment of state attribute (see #53)
• remove old callbacks (see #96)
• remove old aasm DSL (like aasm_state)

Planned changes for AASM >= 3.9

• deprecate old aasm DSL (aasm_state, etc.)
• deprecate old callbacks
• clean-up localization and human methods