add sync: option that allows you to override the way a property is written back to the model in #sync. closes #153.
add Changed which tracks which attributes changed. fixes #117.
document Form#changed?.
that test is working.
copy BaseTest into InheritTest as is gets messed up somewhere else.
always use pass_options.
extract parts of #sync! into #syncable_hash.
start working on Sync::SkipUnchanged to skip unchanged properties in #sync.
add test to assure that :virtual wins over :sync.
ChangedTest is less Dirty.
add tests for form.changed? but don't run them as it's not clear, yet, how to find out if a collection has changed.
backup
wow, Sync::SkipUnchanged seems to work.
"document".
Merge branch 'dirty-sync-option' of github.com:apotonick/reform into dirty-sync-option

Conflicts:
	lib/reform/form/sync.rb
	test/sync_option_test.rb
start removing WithOptions in favour of an explicit Options object being created in the methods that need this abstraction.
RepresenterTest shows a bug in representable: passing both include and exclude breaks.
make SkipUnchanged work with exclude, only!
less complex file requiring. remove virtual_attributes file.
all old tests pass, empty: is now virtual, too.
use minitest 4.2 in rails 4.
allow to hook into #sync via options.